Apparatus and method for recording and reproducing optical information

ABSTRACT

The present invention makes it possible to reduce the size of an optical system for multiplex recording or reproduction of information utilizing holography. 
     A pick-up of an optical information recording/reproducing apparatus generates information light by spatially modulating laser light emitted by a laser source device with a spatial light modulator depending on the information to be recorded and generates reference light for recording having a spatially modulated phase by spatially modulating the phase of laser beam emitted by the light source device with a phase-spatial light modulator. The information light and the reference light for recording are projected upon an optical information recording medium such that they converge in different positions, and information is recorded in the hologram layer in the form of an interference pattern as a result of interference between the information light reflected by a reflecting film and the reference light for recording. The positioning of the information light and the reference light for recording is carried out based on information recorded in address servo areas.

TECHNICAL FIELD

The present invention relates to an optical information recordingapparatus and a method for the same for recording information in anoptical information recording medium utilizing holography, an opticalinformation reproducing apparatus and a method for the same forreproducing information from an optical information recording mediumutilizing holography, an optical information recording/reproducingapparatus for recording information in an optical information recordingmedium and reproducing information from an optical information recordingmedium utilizing holography and an optical information recording mediumin which information is recorded utilizing holography.

BACKGROUND ART

In general, holographic recording for recording information in arecording medium utilizing holography is performed by overlapping lightcarrying image information and reference light in a recording medium andwriting resultant interference fringes in the recording medium. When therecorded information is reproduced, the recording medium is illuminatedwith reference light to cause diffraction attributable to theinterference fringes which reproduces the image information.

Recently, volume holography and, more particularly, digital volumeholography has been developed and is attracting attention in practicalfields for high density optical recording. Volume holography is a methodfor writing interference fringes on a three-dimensional basis byactively using a recording medium even in the direction of the thicknessthereof, which is characterized in that diffracting efficiency isimproved by an increased thickness and in that an increased storagecapacity can be achieved utilizing multiplex recording. Digital volumeholography is a computer-oriented method for holographic recording inwhich image information to be recorded is limited to binary digitalpatterns in spite of the fact that the same recording media andrecording method as the volume holography are used. According to thedigital volume holography, for example, analog image information such asa picture is once digitized to develop two-dimensional digital patterninformation which is in turn recorded as image information. Whenreproduced, the digital pattern information is read and decoded torestore and display the original image information. Since this makes itpossible to perform differential detection and error correction onencoded binary data, the original information can be reproduced withextremely high fidelity even with a somewhat poor SN ratio(signal-to-noise ratio) during reproduction.

FIG. 75 is a perspective view of a schematic configuration of aprior-art recording/reproducing system for digital volume holography.The recording/reproducing system has: a spatial light modulator 101 forgenerating information light 102 based on two-dimensional digitalpattern information; a lens 103 for collecting the information light 102from the spatial light modulator 101 to illuminate a hologram recordingmedium 100 with the same; reference light illumination means (not shown)for illuminating the hologram recording medium 100 with reference light104 in a direction orthogonal to the information light 102; a CCD(charge-coupled device) array 107 for detecting reproducedtwo-dimensional digital pattern information; and a lens 106 forcollecting reproduction light 105 emerging from the hologram recordingmedium 100 to illuminate the CCD array 107 with the same. Crystals ofLiNbO₃ or the like are used for the hologram recording medium 100.

In the recording/reproducing system shown in FIG. 75, recording isperformed by digitizing information of an original image or the like tobe recorded and by arranging the resultant signals having a value of 1or 0 on a two-dimensional basis to generate two-dimensional digitalpattern information. One piece of two-dimensional digital patterninformation is referred to as “page data”. Let us assume here that pagedata #1 through #n are recorded in the same hologram recording medium100 on a multiplex basis. In this case, the spatial light modulator 101first chooses to transmit or block light for each pixel based on thepage data #1 to generate spatially modulated information light 102 withwhich the hologram recording medium 100 is illuminated through the lens103. Simultaneously, the hologram recording medium 100 is illuminatedwith reference light 104 in a direction θ1 substantially orthogonal tothe information light 102 to record interference fringes resulting fromoverlap between the information light 102 and the reference light 104inside the hologram recording medium 100. In order to improvediffracting efficiency, the reference light 104 is transformed by acylindrical lens or the like into flat beams to record the interferencefringes in the hologram recording medium 100 even in the direction ofthe thickness thereof. To record the next page data #2, the referencelight 104 is projected at an angle θ2 different from θ1 and isoverlapped with the information light 102 to perform multiplex recordingof information in the same hologram recording medium 100. Similarly, torecord the other page data #3 through #n, the reference light 104 isprojected at respective different angles θ3 through θn to recordinformation on a multiplex basis. Such a hologram having informationrecorded therein on a multiplex basis is referred to as “stack”. In theexample shown in FIG. 75, the hologram recording medium 100 has aplurality of stacks (stack 1, stack 2, . . . , stack m, . . . ).

Arbitrary page data can be reproduced from a stack by illuminating thestack with reference light 104 at the same incident angle as that forthe recording of the page data. As a result, the reference light 104 isselectively diffracted by interference fringes associated with the pagedata to generate reproduction light 105. The reproduction light 105impinges upon the CCD array 107 through the lens 106, and the CCD array107 detects a two-dimensional pattern of the reproduction light. Thedetected two-dimensional pattern of the reproduction light is decodedconversely to the process performed during recording so that informationsuch as an original image is reproduced.

While the configuration shown in FIG. 75 allows multiplex recording ofinformation in the same hologram recording medium 100, in order torecord information with a high density, the positioning of theinformation light 102 and reference light 104 in the hologram recordingmedium 100 is important. In the configuration shown in FIG. 75, however,since the hologram recording medium 100 itself carries no informationfor positioning, there is only a mechanical way to position theinformation light 102 and reference light 104 on the hologram recordingmedium 100, which makes it difficult to perform the positioning withhigh accuracy. This has resulted in problems in that removability (theease of performing recording and reproduction of a hologram recordingmedium on a recording/reproducing apparatus after moving it from anotherrecording/reproducing apparatus with the same results as on the previousapparatus) is poor; random access is difficult; and high densityrecording is difficult. The configuration shown in FIG. 75 has anotherproblem in that it involves a large optical system for recording orreproduction because the optical axes of the information light 102,reference light 104 and reproduction light 105 are located in differentspatial positions.

Various methods for multiplex recording have been proposed in an attemptto increase the recording capacity of holographic recording by improvingthe recording density. One of such methods is angle multiplexing asshown in FIG. 75. However, such angle multiplexing has a problemparticularly in that it involves a large and complex optical system forrecording or reproduction because the angle of the reference light mustbe varied.

In addition to the above-described angle multiplex, proposed prior-artmethods for multiplex recording for holographic recording include:phase-encoding multiplexing as disclosed, for example, in an article ofJ. F. Heanue et al., “Recall of linear combinations of stored data pagesbased on phase-code multiplexing in volume holography”, Optics Letters,Vol. 19, No. 14, pp. 1079–1081, 1994 and an article of J. F. Heanue etal., “Encrypted holographic data storage based onorthogonal-phase-encoding multiplexing”, Applied Optics, Vol. 34, No.26, pp. 6012–6015, 1995; and hole burning type wavelength multiplexingas disclosed, for example, in an article by Eiji YAGYU et al., “The NewRealtime 3-D Imaging Technique by the Frequency Multiplexed PHBHologram”, Technical Report of IEICE, EDI93–87, HC93-54, pp. 1–5, 1993.

In any of the methods for multiplex recording, optical systems forrecording or reproduction proposed in prior art have a problem in thattheir size is increased by the fact that the optical axes of informationlight, reference light and reproduction light are located in spatiallydifferent positions and in that a dramatic improvement in the recordingdensity is not achievable because the hologram recording mediathemselves have no information for positioning and it is thereforedifficult to position light for recording or reproduction on thehologram recording media with high accuracy.

DISCLOSURE OF THE INVENTION

The present invention has been conceived taking such problems intoconsideration, and it is a first object of the invention to provide anapparatus and a method for recording optical information capable ofperforming multiplex recording of information in an optical informationrecording medium in which information is recorded utilizing holographyand an apparatus and a method for reproducing optical information toreproduce information from an optical information recording mediumcarrying information recorded in such a manner, in which an opticalsystem for recording or reproducing can be compactly configured.

In addition to the above-described first object, it is a second objectof the invention to provide an apparatus and a method for recordingoptical information and an apparatus and a method for reproducingoptical information, in which light for recording or reproduction can beaccurately positioned relative to an optical information recordingmedium.

It is a third object of the invention to provide an optical informationrecording apparatus for recording information in an optical informationrecording medium utilizing holography, an optical informationreproducing apparatus for reproducing information from an opticalinformation recording medium utilizing holography and an opticalinformation recording/reproducing apparatus for recording information inand reproducing information from an optical information recording mediumutilizing holography, in which an optical system for recording orreproduction can be compactly configured and in which random access tothe optical information recording medium is facilitated.

It is a fourth object of the invention to provide an optical informationrecording medium for recording information utilizing holography withwhich random access and high density recording can be easily achieved.

A first optical information recording apparatus according to theinvention is an optical information recording apparatus for recordinginformation in an optical information recording medium having aninformation recording layer in which information is recorded utilizingholography, the apparatus comprising: information light generation meansfor generating information light carrying information; recordingreference light generation means including phase modulation means forspatially modulating the phase of light, for generating reference lightfor recording whose phase has been spatially modulated by the phasemodulation means; and a recording optical system for illuminating theinformation recording layer on the same side thereof with theinformation light generated by the information light generation meansand the reference light for recording generated by the recordingreference light generation means such that the information is recordedin the information recording layer in the form of an interferencepattern as a result of interference between the information light andthe reference light for recording.

A first method for recording optical information according to theinvention is a method for recording information in an opticalinformation recording medium having an information recording layer inwhich information is recorded utilizing holography, the methodcomprising the steps of: generating information light carryinginformation; spatially modulating the phase of light to generatereference light for recording having a spatially modulated phase; andilluminating the information recording layer on the same side thereofwith the information light and the reference light for recording torecord the information in the information recording layer in the form ofan interference pattern as a result of interference between theinformation light and the reference light for recording.

In the first apparatus or method for recording optical informationaccording to the invention, the information recording layer isilluminated on the same side thereof with the information light carryinginformation and the reference light for recording having a spatiallymodulated phase to record the information in the information recordinglayer in the form of an interference pattern as a result of interferencebetween the information light and the reference light for recording.

A first optical information reproducing apparatus according to theinvention is an optical information reproducing apparatus forreproducing information utilizing holography from an optical informationrecording medium having an information recording layer in which theinformation is recorded in the form of an interference pattern as aresult of interference between information light carrying theinformation and reference light for recording having a spatiallymodulated phase, the apparatus comprising: reproduction reference lightgeneration means including phase modulation means for spatiallymodulating the phase of light, for generating reference light forreproduction having a phase spatially modulated by the phase modulationmeans; a reproducing optical system for illuminating the informationrecording layer with the reference light for reproduction generated bythe reproduction reference light generation means and for collectingreproduction light generated at the information recording layer whenilluminated with the reference light for reproduction on the same sideof the information recording layer that is illuminated with thereference light for reproduction; and detection means for detecting thereproduction light collected by the reproducing optical system.

A first method for reproducing optical information according to theinvention is a method for reproducing information utilizing holographyfrom an optical information recording medium having an informationrecording layer in which the information is recorded in the form of aninterference pattern as a result of interference between informationlight carrying the information and reference light for recording havinga spatially modulated phase, the method comprising the steps of:spatially modulating the phase of light to generate reference light forreproduction having a spatially modulated phase; illuminating theinformation recording layer with the reference light for reproductionand collecting reproduction light generated at the information recordinglayer when illuminated with the reference light for reproduction on thesame side of the information recording layer that is illuminated withthe reference light for reproduction; and detecting the collectedreproduction light.

In the first apparatus or method for reproducing optical informationaccording to the invention, the information recording layer isilluminated with the reference light for reproduction having a spatiallymodulated phase; reproduction light generated at the informationrecording layer when illuminated with the reference light forreproduction is collected on the same side of the information recordinglayer that is illuminated with the reference light for reproduction; andthe collected reproduction light is detected.

A second optical information recording apparatus according to theinvention is an optical information recording apparatus for recordinginformation in an optical information recording medium having aninformation recording layer in which a change in absorbance occurs in anabsorption spectrum thereof in the position of a wavelength of incidentlight and in which information is recorded utilizing holography, theapparatus comprising: wavelength selection means for selecting awavelength of light illuminating the information recording layer fromamong a plurality of wavelengths; information light generation means forgenerating information light having the wavelength selected by thewavelength selection means and carrying information; recording referencelight generation means for generating reference light for recordinghaving the wavelength selected by the wavelength selection means; and arecording optical system for illuminating the information recordinglayer on the same side thereof with the information light generated bythe information light generation means and the reference light forrecording generated by the recording reference light generation meanssuch that the information is recorded in the information recording layerin the form of an interference pattern as a result of interferencebetween the information light and the reference light for recording.

A second method for recording optical information according to theinvention is a method for recording information in an opticalinformation recording medium having an information recording layer inwhich a change in absorbance occurs in an absorption spectrum thereof inthe position of a wavelength of incident light and in which informationis recorded utilizing holography, the method comprising the steps of:selecting a wavelength of light illuminating the information recordinglayer from among a plurality of wavelengths; generating informationlight having the selected wavelength and carrying information;generating reference light for recording having the selected wavelength;and illuminating the information recording layer on the same sidethereof with the information light and the reference light for recordingto record the information in the information recording layer in the formof an interference pattern as a result of interference between theinformation light and the reference light for recording.

In the second apparatus or method for recording optical informationaccording to the invention, the information recording layer isilluminated on the same side thereof with the information light havingthe selected wavelength and carrying information and the reference lightfor recording having the selected wavelength to record the informationin the information recording layer in the form of an interferencepattern as a result of interference between the information light andthe reference light for recording.

A second optical information reproducing apparatus according to theinvention is an optical information reproducing apparatus forreproducing information utilizing holography from an optical informationrecording medium having an information recording layer in which theinformation is recorded in the form of an interference pattern as aresult of interference between information light having a wavelengthselected from among a plurality of wavelengths and carrying theinformation and reference light for recording having the wavelengthselected from among a plurality of wavelengths, the apparatuscomprising: wavelength selection means for selecting a wavelength oflight illuminating the information recording layer from among aplurality of wavelengths; reproduction reference light generation meansfor generating reference light for reproduction having the wavelengthselected by the wavelength selection means; a reproducing optical systemfor illuminating the information recording layer with the referencelight for reproduction generated by the reproduction reference lightgeneration means and for collecting reproduction light generated at theinformation recording layer when illuminated with the reference lightfor reproduction on the same side of the information recording layerthat is illuminated with the reference light for reproduction; anddetection means for detecting the reproduction light collected by thereproducing optical system.

A second method for reproducing optical information is an opticalinformation reproducing method for reproducing information utilizingholography from an optical information recording medium having aninformation recording layer in which the information is recorded in theform of an interference pattern as a result of interference betweeninformation light having a wavelength selected from among a plurality ofwavelengths and carrying the information and reference light forrecording having the wavelength selected from among a plurality ofwavelengths, the method comprising the steps of: selecting a wavelengthof light illuminating the information recording layer from among aplurality of wavelengths; generating reference light for reproductionhaving the selected wavelength; illuminating the information recordinglayer with the reference light for reproduction and collectingreproduction light generated at the information recording layer whenilluminated with the reference light for reproduction on the same sideof the information recording layer that is illuminated with thereference light for reproduction; and detecting the collectedreproduction light.

In the second apparatus or method for reproducing optical informationaccording to the invention, the information recording layer isilluminated with the reference light for reproduction having theselected wavelength; reproduction light generated at the informationrecording layer when illuminated with the reference light forreproduction is collected on the same side of the information recordinglayer that is illuminated with the reference light for reproduction; andthe collected reproduction light is detected.

A third optical information recording apparatus according to theinvention is an optical information recording apparatus for recordinginformation in an optical information recording medium having aninformation recording layer in which a change in absorbance occurs in anabsorption spectrum thereof in the position of a wavelength of incidentlight and in which information is recorded utilizing holography, theapparatus comprising: wavelength selection means for selecting awavelength of light illuminating the information recording layer fromamong a plurality of wavelengths; information light generation means forgenerating information light having the wavelength selected by thewavelength selection means and carrying information; recording referencelight generation means including phase modulation means for spatiallymodulating the phase of light, for generating reference light forrecording having the wavelength selected by the wavelength selectionmeans and having a phase spatially modulated by the phase modulationmeans; and a recording optical system for illuminating the informationrecording layer on the same side thereof with the information lightgenerated by the information light generation means and the referencelight for recording generated by the recording reference lightgeneration means such that the information is recorded in theinformation recording layer in the form of an interference pattern as aresult of interference between the information light and the referencelight for recording.

A third method for recording optical information according to theinvention is an optical information recording method for recordinginformation in an optical information recording medium having aninformation recording layer in which a change in absorbance occurs in anabsorption spectrum thereof in the position of a wavelength of incidentlight and in which information is recorded utilizing holography, themethod comprising the steps of: selecting a wavelength of lightilluminating the information recording layer from among a plurality ofwavelengths; generating information light having the selected wavelengthand carrying information; spatially modulating the phase of light togenerate reference light for recording having the selected wavelengthand a spatially modulated phase; and illuminating the informationrecording layer on the same side thereof with the information light andthe reference light for recording to record the information in theinformation recording layer in the form of an interference pattern as aresult of interference between the information light and the referencelight for recording.

In the third apparatus or method for recording optical informationaccording to the invention, the information recording layer isilluminated on the same side thereof with the information light havingthe selected wavelength and carrying information and the reference lightfor recording having the selected wavelength and a spatially modulatedphase to record the information in the information recording layer inthe form of an interference pattern as a result of interference betweenthe information light and the reference light for recording.

A third optical information reproducing apparatus according to theinvention is an optical information reproducing apparatus forreproducing information utilizing holography from an optical informationrecording medium having an information recording layer in which theinformation is recorded in the form of an interference pattern as aresult of interference between information light having a wavelengthselected from among a plurality of wavelengths and carrying theinformation and reference light for recording having the wavelengthselected from among a plurality of wavelengths and having a spatiallymodulated phase, the apparatus comprising: wavelength selection meansfor selecting a wavelength of light illuminating the informationrecording layer from among a plurality of wavelengths; reproductionreference light generation means including phase modulation means forspatially modulating the phase of light, for generating reference lightfor reproduction having the wavelength selected by the wavelengthselection means and having a phase spatially modulated by the phasemodulation means; a reproducing optical system for illuminating theinformation recording layer with the reference light for reproductiongenerated by the reproduction reference light generation means and forcollecting reproduction light generated at the information recordinglayer when illuminated with the reference light for reproduction on thesame side of the information recording layer that is illuminated withthe reference light for reproduction; and detection means for detectingthe reproduction light collected by the reproducing optical system.

A third method for reproducing optical information according to theinvention is an optical information reproducing method for reproducinginformation utilizing holography from an optical information recordingmedium having an information recording layer in which the information isrecorded in the form of an interference pattern as a result ofinterference between information light having a wavelength selected fromamong a plurality of wavelengths and carrying the information andreference light for recording having the wavelength selected from amonga plurality of wavelengths and having a spatially modulated phase, themethod comprising the steps of: selecting a wavelength of lightilluminating the information recording layer from among a plurality ofwavelengths; spatially modulating the phase of light to generatereference light for reproduction having the selected wavelength and aspatially modulated phase; illuminating the information recording layerwith the reference light for reproduction and collecting reproductionlight generated at the information recording layer when illuminated withthe reference light for reproduction on the same side of the informationrecording layer that is illuminated with the reference light forreproduction; and detecting the collected reproduction light.

In the third apparatus or method for reproducing optical information,the information recording layer is illuminated with the reference lightfor reproduction having the selected wavelength and spatially modulatedphase; reproduction light generated at the information recording layerwhen illuminated with the reference light for reproduction is collectedon the same side of the information recording layer that is illuminatedwith the reference light for reproduction; and the collected light isdetected.

A fourth optical information recording apparatus according to theinvention is an optical information recording apparatus for recordinginformation in an optical information recording medium having aninformation recording layer in which information is recorded utilizingholography, the apparatus comprising a pick-up device provided in aface-to-face relationship with the optical information recording medium,the pick-up device having: a light source for emitting beams of light;information light generation means for spatially modulating the beams oflight emitted by the light source to generate information light carryinginformation; recording reference light generation means for generatingreference light for recording using the beams of light emitted by thelight source; and a recording optical system for illuminating theinformation recording layer on the same side thereof with theinformation light generated by the information light generation meansand the reference light for recording generated by the recordingreference light generation means such that the information is recordedin the information recording layer in the form of an interferencepattern as a result of interference between the information light andthe reference light for recording.

In the fourth optical information recording apparatus according to theinvention, the pick-up device provided in a face-to-face relationshipwith the optical information recording medium illuminates theinformation recording layer on the same side thereof with theinformation light and the reference light for recording to record theinformation in the information recording layer in the form of aninterference pattern as a result of interface between the informationlight and the reference light for recording.

A fourth optical information reproducing apparatus according to theinvention is an optical information reproducing apparatus forreproducing information from an optical information recording mediumhaving an information recording layer with information recorded thereinutilizing holography, the apparatus comprising a pick-up device providedin a face-to-face relationship with the optical information recordingmedium, the pick-up device having: a light source for emitting beams oflight; reproduction reference light generation means for generatingreference light for reproduction using the beams of light emitted by thelight source; a reproducing optical system for illuminating theinformation recording layer with the reference light for reproductiongenerated by the reproduction reference light generation means and forcollecting reproduction light generated at the information recordinglayer when illuminated with the reference light for reproduction on thesame side of the information recording layer that is illuminated withthe reference light for reproduction; and detection means for detectingthe reproduction light collected by the reproducing optical system.

In the fourth optical information reproducing apparatus according to theinvention, the pick-up device provided in a face-to-face relationshipwith the optical information recording medium illuminates theinformation recording layer with the reference light for reproduction;reproduction light generated at the information recording layer whenilluminated with the reference light for reproduction is collected onthe same side of the information recording layer that is illuminatedwith the reference light for reproduction; and the collected referencelight is detected.

An optical information recording/reproducing apparatus according to thepresent invention is an optical information recording/reproducingapparatus for recording information in an optical information recordingmedium having an information recording layer in which information isrecorded utilizing holography and for reproducing the information fromthe optical information recording medium, the apparatus comprising apick-up device provided in a face-to-face relationship with the opticalinformation recording medium, the pick-up device having: a light sourcefor emitting beams of light; information light generation means forgenerating information light carrying information by spatiallymodulating the beams of light emitted by the light source; recordingreference light generation means for generating reference light forrecording using the beams of light emitted by the light source;reproduction reference light generation means for generating referencelight for reproduction using the beams of light emitted by the lightsource; a recording/reproducing optical system for illuminating theinformation recording layer on the same side thereof with theinformation light generated by the information light generation meansand the reference light for recording generated by the recordingreference light generation means such that the information is recordedin the information recording layer in the form of an interferencepattern as a result of interference between the information light andthe reference light for recording, for illuminating the informationrecording layer with the reference light for reproduction generated bythe reproduction reference light generation means and for collectingreproduction light generated at the information recording layer whenilluminated with the reference light for reproduction on the same sideof the information recording layer that is illuminated with thereference light for reproduction; and detection means for detecting thereproduction light collected by the reproducing/reproducing opticalsystem.

In the optical information recording/reproducing apparatus according tothe invention, during recording, the pick-up device provided in aface-to-face relationship with the optical information recording mediumprojects the information light and the reference light for recordingupon the information recording layer on the same side thereof to recordinformation in the information recording layer using an interferencepattern as a result of interference between the information light andthe reference light for recording. During reproduction, the pick-updevice illuminates the information recording layer with the referencelight for reproduction; reproduction light generated at the informationrecording light when illuminated with the reference light forreproduction is collected on the same side of the information recordinglayer that is illuminated with the reference light for reproduction; andthe collected reproduction light is detected.

An optical information recording medium according to the inventioncomprises: a first information layer for recording information in theform of an interference pattern as a result of interference betweeninformation light and reference light for recording utilizing holographyand for generating reproduction light associated with the recordedinformation when illuminated with reference light for reproduction; anda second information layer which is provided in a position differentfrom the position of the first information layer in the direction of thethickness and in which information is recorded using means differentfrom that for the recording of information in the first informationlayer.

In the optical information recording medium according to the invention,information is recorded in the first recording layer in the form of aninterference pattern as a result of interference between informationlight and reference light for recording utilizing holography, andinformation is recorded in the second recording layer using means otherthan that for recording of information in the first information layer.

Other objects, features and objectives of the invention will becomesufficiently clear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing a configuration of a pick-up of anoptical information recording/reproducing apparatus according to a firstembodiment and a configuration of an optical information recordingmedium.

FIG. 2 is a block diagram of a general configuration of the opticalinformation recording/reproducing apparatus according to the firstembodiment.

FIG. 3 is a block diagram of a configuration of the detection circuit inFIG. 2.

FIG. 4 is an illustration of a state of the pick-up shown in FIG. 1during servo.

FIG. 5 is an illustration for explaining polarized beams used in thefirst embodiment of the invention.

FIG. 6 is an illustration of a state of the pick-up shown in FIG. 1during recording.

FIG. 7 is an illustration of a state of light in the pick-up in thestate shown in FIG. 6.

FIG. 8 is an illustration of a state of light in the pick-up in thestate shown in FIG. 6.

FIG. 9 is an illustration of a state of the pick-up shown in FIG. 1during reproduction.

FIG. 10 is an illustration of a state of light in the pick-up in thestate shown in FIG. 9.

FIG. 11 is an illustration of a state of light in the pick-up in thestate shown in FIG. 9.

FIGS. 12A and 12B are illustrations for explaining a method forrecognizing a reference position in a pattern of reproduction light fromdata detected by the CCD array in FIG. 1.

FIGS. 13A and 13B are illustrations for explaining a method forrecognizing a reference position in a pattern of reproduction light fromdata detected by the CCD array in FIG. 1.

FIGS. 14A and 14B are illustrations of a pattern of information lightand a pattern of reproduction light in the pick-up shown in FIG. 1.

FIGS. 15A and 15B illustrate the contents of data determined from apattern of reproduction light detected by the pick-up shown in FIG. 1and an ECC table associated with the data.

FIG. 16 is a characteristics diagram showing a state of the absorptionspectrum of a hole burning material in which a reduction of absorbancehas occurred in a plurality of wavelength positions as a result ofillumination with light having a plurality of wavelengths.

FIG. 17 is an illustration of a configuration of a pick-up according toa third embodiment of the invention.

FIG. 18 is a plan view of a configuration of an optical unit includingvarious elements that form the pick-up according to the third embodimentof the invention.

FIGS. 19A and 19B are illustrations of an example of the rotatingoptical element in FIG. 17.

FIG. 20 is an illustration of a configuration of a pick-up which can uselaser light in three colors according to the third embodiment of theinvention.

FIG. 21 is a plan view of a slide-feed mechanism of the optical unitshown in FIG. 18.

FIG. 22 is a partially cutaway side view of the slide-feed mechanismshown in FIG. 21 in a stationary state.

FIG. 23 is a partially cutaway side view of the slide-feed mechanismshown in FIG. 21 with the optical unit displaced slightly.

FIGS. 24A through 24C are illustrations of an operation of the actuatorshown in FIG. 21.

FIG. 25 is an illustration showing a moving direction of an objectivelens of the pick-up shown in FIG. 17 during a seek and a movingdirection of the same during in-field access.

FIGS. 26A and 26B are illustrations for explaining the positioning ofreference light and information light in a third embodiment of theinvention.

FIG. 27 is an illustration of an example of a locus of the center of theobjective lens in the case of access to a plurality of locations of anoptical information recording medium utilizing a seeking movement andin-field access in combination in the third embodiment of the invention.

FIG. 28 is a plan view of a cartridge for containing the opticalinformation recording medium in the third embodiment of the invention.

FIG. 29 is a plan view of the cartridge shown in FIG. 28 with a shutterthereof opened.

FIG. 30 is a plan view showing an example wherein two optical units areprovided in a face-to-face relationship with one side of the opticalinformation recording medium in the third embodiment of the invention.

FIG. 31 is a plan view showing an example wherein four optical units areprovided in the third embodiment of the invention.

FIG. 32 is a sectional view taken along the line A–A′ in FIG. 31.

FIG. 33 is a sectional view taken along the line B–B′ in FIG. 31.

FIG. 34 is a plan view showing an example wherein sixteen optical unitsare provided in the third embodiment of the invention.

FIG. 35 is a sectional view of one half of an air gap type opticalinformation recording medium according to the third embodiment of theinvention.

FIG. 36 is an exploded perspective view of the one half of the air gaptype optical information recording medium in the third embodiment of theinvention.

FIG. 37 is a perspective view of the one half of the air gap typeoptical information recording medium in the third embodiment of theinvention.

FIG. 38 is a sectional view of one half of a transparent substrate gaptype optical information recording medium according to the thirdembodiment of the invention.

FIG. 39 is an exploded perspective view of the one half of thetransparent substrate gap type optical information recording medium inthe third embodiment of the invention.

FIG. 40 is a perspective view of the one half of the transparentsubstrate gap type optical information recording medium in the thirdembodiment of the invention.

FIG. 41 is a sectional view of a single-sided 1.2 mm thickness typeoptical information recording medium according to the third embodimentof the invention.

FIG. 42 is a sectional view of a single-sided 0.6 mm thickness typeoptical information recording medium according to the third embodimentof the invention.

FIG. 43 is an illustration of how to illuminate a single-sided opticalinformation recording medium as shown in FIG. 41 or 42 with referencelight for recording and information light.

FIG. 44 is a sectional view of a double-sided transparent substrate gaptype optical information recording medium according to the thirdembodiment of the invention.

FIG. 45 is a sectional view of a double-sided air gap type opticalinformation recording medium according to the third embodiment of theinvention.

FIG. 46 is an illustration of how to illuminate a double-sided opticalinformation recording medium as shown in FIG. 44 or 45 with referencelight for recording and information light.

FIG. 47 is an illustration of a single-sided type optical disk.

FIG. 48 is an illustration of the use of the optical disk shown in FIG.47 in the optical information recording/reproducing apparatus accordingto the third embodiment of the invention.

FIG. 49 is an illustration of a double-sided type optical disk.

FIG. 50 is an illustration of the use of the optical disk shown in FIG.49 in the optical information recording/reproducing apparatus accordingto the third embodiment of the invention.

FIG. 51 is a perspective view of a common recording/reproducing systemthat performs phase-encoding multiplexing showing a schematicconfiguration thereof.

FIGS. 52A through 52C are illustrations showing how interference fringesare formed in a hologram recording medium as a result of interferencebetween information light and reference light.

FIG. 53 is an illustration of a state of the pick-up of the thirdembodiment of the invention during a servo operation.

FIG. 54 is an illustration of a state of light in the vicinity of anoptical disk in the case of recording and reproduction using a normaloptical disk with the optical information recording/reproducingapparatus according to the third embodiment of the invention.

FIG. 55 is an illustration of a state of the pick-up of the thirdembodiment of the invention during recording.

FIG. 56 is an illustration of a state of light in the vicinity of theoptical information recording medium of the third embodiment of theinvention during recording.

FIG. 57 is an illustration of a state of light in the vicinity of theoptical information recording medium of the third embodiment of theinvention during recording.

FIG. 58 is an illustration of a state of the pick-up of the thirdembodiment of the invention during fixing.

FIG. 59 is an illustration of a state of light in the vicinity of theoptical information recording medium of the third embodiment of theinvention during fixing.

FIG. 60 is an illustration of a state of the pick-up of the thirdembodiment of the invention during reproduction.

FIG. 61 is an illustration of a state of light in the vicinity of theoptical information recording medium of the third embodiment of theinvention during reproduction.

FIG. 62 is an illustration of a state of light in the vicinity of theoptical information recording medium of the third embodiment of theinvention during reproduction.

FIG. 63 is an illustration for explaining a direct read after writefunction and a write power control function during multiplex recordingof the optical information recording/reproducing apparatus of the thirdembodiment of the invention.

FIG. 64 is a block diagram showing a circuit configuration required forperforming verification in the optical information recording/reproducingapparatus according to the third embodiment of the invention.

FIG. 65 is an illustration of an example of a distributed recordingmethod in the third embodiment of the invention.

FIG. 66 is an illustration of another example of a distributed recordingmethod in the third embodiment of the invention.

FIG. 67 is an illustration of still another example of a distributedrecording method in the third embodiment of the invention.

FIG. 68 is an illustration of an example of an arrangement of aplurality of interference regions used in the distributed recordingmethods in the third embodiment of the invention.

FIG. 69 is an illustration of another example of an arrangement of aplurality of interference regions used in the distributed recordingmethods in the third embodiment of the invention.

FIG. 70 is an illustration for explaining a distributed recording methodin recording a plurality of items of data on a multiplex basis utilizingshift multiplexing in the third embodiment of the invention.

FIG. 71 is an illustration for explaining a distributed recording methodin recording a plurality of items of data on a multiplex basis utilizingphase-encoding multiplexing and shift multiplexing in combination in thethird embodiment of the invention.

FIG. 72 is a perspective view of the exterior of a juke apparatus as anexample of application of the optical information recording/reproducingapparatus according to the third embodiment of the invention.

FIG. 73 is a block diagram showing a circuit configuration of the jukeapparatus shown in FIG. 72

FIG. 74 is a block diagram of an example of a configuration of majorparts in a case in which a phase modulation pattern for reference lightis created based on information specific to a person in the opticalinformation recording/reproducing apparatus according to the thirdembodiment of the invention.

FIG. 75 is a perspective view of a prior-art recording/reproducingsystem of digital volume holography to show a schematic configuration ofthe same.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the drawings. A first embodiment of the invention isan example in which multiplex recording is realized using phase encodingmultiplexing. FIG. 1 is an illustration showing a configuration of apick-up of an optical information recording/reproducing apparatus as anoptical information recording apparatus and an optical informationreproducing apparatus according to the present embodiment and aconfiguration of an optical information recording medium according tothe present embodiment. FIG. 2 is a block diagram of a generalconfiguration of the optical information recording/reproducing apparatusaccording to the present embodiment.

First, the configuration of the optical information recording mediumaccording to the present embodiment will be described with reference toFIG. 1. The optical information recording medium 1 is configured byforming: a hologram layer 3 as an information recording layer forrecording information utilizing volume holography; a reflecting film 5;and a protective film 4 in the order listed on one surface of adisk-shaped transparent substrate 2 formed from polycarbonate or thelike. A plurality of address servo areas 6 as positioning regionsextending linearly in the radial direction are provided at predeterminedangular intervals at the interface between the hologram layer 3 and theprotective layer 4. Sections in the form of sectors between theadjoining address servo areas 6 are data areas 7. Information forperforming focus servo and tracking servo using a sampled servo systemand address information are recorded in advance in the form of embosspits in the address servo areas 6. Focus servo can be performed using areflecting surface of the reflecting film 5. For example, wobble pitsmay be used as the information for performing tracking servo. Forexample, the transparent substrate 2 has an appropriate thickness of 0.6mm or less, and the hologram layer 3 has an appropriate thickness of 10μm or more. The hologram layer 3 is formed of a hologram material whoseoptical characteristics such as are fractive index, permittivity andreflectivity change depending on the intensity of light when illuminatedwith the light. For example, photopolymer HRF-600 (product name)manufactured by DuPont or the like is used as such a hologram material.For example, the reflecting film 5 is formed of aluminum.

The configuration of the optical information recording/reproducingapparatus according to the present embodiment will now be described withreference to FIG. 2. An optical information recording/reproducingapparatus 10 has: a spindle 81 to which the optical informationrecording medium 1 is mounted; a spindle motor 82 for rotating thespindle 81; and a spindle servo circuit 83 for controlling the spindlemotor 82 to keep the rotating speed of the optical information recordingmedium 1 at a predetermined value. The optical informationrecording/reproducing apparatus 10 further has: a pick-up 11 forrecording information in the optical information recording medium 1 byilluminating it with information light and recording reference light andfor reproducing the information recorded in the optical informationrecording medium 1 by illuminating the optical information recordingmedium 1 with reference light for reproduction and by detectingreproduction light; and a driver 84 for allowing the pick-up 11 to movein the radial direction of the optical information recording medium 1.

The optical information recording/reproducing apparatus 10 further has:a detection circuit 85 for detecting a focus error signal FE, a trackingerror signal TE and a reproduction signal RF from a signal output by thepick-up 11; a focus servo circuit 86 for performing focus servo bydriving an actuator in the pick-up 11 based on the focus error signal FEdetected by the detection circuit 85 to move an objective lens in thedirection of the thickness of the optical information recording medium1; a tracking servo circuit 87 for performing tracking servo by drivingthe actuator in the pick-up 11 based on the tracking error signal TEdetected by the detection circuit 85 to move the objective lens in theradial direction of the optical information recording medium 1; and aslide servo circuit 88 for performing slide servo by controlling thedriver 84 based on the tracking error signal TE and a command from acontroller to be described later to move the pick-up 11 in the radialdirection of the optical information recording medium 1.

The optical information recording/reproducing apparatus 10 further has:a signal processing circuit 89 for reproducing data recorded in the dataareas 7 of the optical information recording medium 1 by decoding dataoutput by a CCD array to be described later in the pick-up 11 and forreproducing a basic clock and determining an address from thereproduction signal RF from the detection circuit 85; a controller 90for controlling the optical information recording/reproducing apparatus10 as a whole; and an operating portion 91 for supplying variousinstructions to the controller 90. The controller 90 receives input ofthe basic clock and address information output by the signal processingcircuit 89 and controls the pick-up 11, spindle servo circuit 83, slideservo circuit 88 and the like. The basic clock output by the signalprocessing circuit 89 is input to the spindle servo circuit 83. Thecontroller 90 has a CPU (central processing unit), a ROM (read onlymemory) and a RAM (random access memory), and the CPU executes programsstored in the ROM using the RAM as a work area to realize the functionsof the controller 90.

The detection circuit 85, focus servo circuit 86, tracking servo circuit87 and slide servo circuit 88 correspond to the position control meansaccording to the invention.

A configuration of the pick-up 11 of the present embodiment will now bedescribed with reference to FIG. 1. The pick-up 11 has: an objectivelens 12 which faces the transparent substrate 2 of the opticalinformation recording medium 1 when the optical information recordingmedium 1 is secured to the spindle 81; an actuator 13 capable of movingthe objective lens 12 in the direction of the thickness of the opticalinformation recording medium 1 and the radial direction of the same; anda double optically rotating plate 14 and a prism block 15 which aredisposed on the side of the objective lens 12 opposite to the opticalinformation recording medium 1 in the order listed which is the order oftheir closeness to the objective lens 12. The double optically rotatingplate 14 has: an optically rotating plate 14L provided on the left sideof the optical axis in FIG. 1; and an optically rotating plate 14Rprovided on the right side of the optical axis in FIG. 1. The opticallyrotating plate 14L optically rotates a polarizing direction at +45°, andthe optically rotating plate 14R optically rotates a polarizingdirection at −45°. The prism block 15 has a half-reflecting surface 15 aand a reflecting surface 15 b which are arranged in the order listedwhich is the order of their closeness to the double optically rotatingplate 14. The normal directions of both of the half-reflecting surface15 a and the reflecting surface 15 b are at 45° to the direction of theoptical axis of the objective lens 12 and are in parallel with eachother.

The pick-up 11 further has a prism block 19 provided on a side of theprism block 15. The prism block 19 has: a reflecting surface 19 a whichis provided in a position associated with the half-reflecting surface 15a of the prism block 15 and which is in parallel with thehalf-reflecting surface 15 a; and a half-reflecting surface 19 b whichis provided in a position associated with the reflecting surface 15 band which is in parallel with the reflecting surface 15 b.

The pick-up 11 further has a convex lens 16 and a phase-spatial lightmodulator 17 which are provided between the prism blocks 15 and 19 inpositions associated with the half-reflecting surface 15 a andreflecting surface 19 a, and has a spatial light modulator 18 providedbetween the prism blocks 15 and 19 in a position associated with thereflecting surface 15 b and the half-reflecting surface 19 b.

The phase-spatial light modulator 17 has a multiplicity of pixelsarranged in the form of a grid and is capable of spatially modulatingthe phase of light by selecting a phase for light emitted by each of thepixels. A liquid crystal element may be used as the phase-spatial lightmodulator 17. The phase-spatial light modulator 17 corresponds to thephase modulation means according to the invention.

The spatial light modulator 18 has a multiplicity of pixels arranged inthe form of a grid and is capable of generating information lightcarrying information by spatially modulating light in terms of intensityby selecting a light transmitting state or a light blocking state foreach of the pixels. A liquid crystal element may be used as the spatiallight modulator 18. The spatial light modulator 18 constitutes theinformation light generation means according to the invention.

The pick-up 11 further has a CCD array 20 as detection means provided ina direction in which return light from the optical information recordingmedium 1 is reflected by the half-reflecting surface 19 b of the prismblock 19 after being transmitted by the spatial light modulator 18.

The pick-up 11 further has a beam splitter 23, a collimator lens 24 anda light source device 25 which are provided on the side of the prismblock 19 opposite to the spatial light modulator 18 in the order listedwhich is the order of their closeness to the prism block 19. The beamsplitter 23 has a half-reflecting surface 23 a whose normal direction istilted at an angle of 45° to the direction of the optical axis of thecollimator lens 24. The light source device 25 emits coherent linearlypolarized light and may be, for example, a semiconductor laser.

The pick-up 11 further has: a photodetector 26 provided in a directionin which light from the light source device 25 is reflected by thehalf-reflecting surface 23 a of the beam splitter 23; and a convex lens27, a cylindrical lens 28 and a quadruple photodetector 29 which areprovided on the side of the beam splitter 23 opposite to thephotodetector 26 in the order listed which is the order of theircloseness to the beam splitter 23. The photodetector 26 receives lightfrom the light source device 25, and the output of the same is used toadjust the output of the light source device 25 automatically. As shownin FIG. 3, the quadruple photodetector 29 has four light-receivingportions 29 a through 29 d divided by a division line 30 a in parallelwith a direction corresponding to the direction of tracks of the opticalinformation recording medium 1 and a division line 30 b orthogonalthereto. The cylindrical lens 28 is provided such that the central axisof the cylindrical surface thereof is at an angle of 45° to the divisionlines 30 a and 30 b of the quadruple photodetector 29.

The phase-spatial light modulator 17, the spatial light modulator 18 andthe light source device 25 in the pick-up 11 are controlled by thecontroller 90 in FIG. 2. The controller 90 has information of aplurality of modulation patterns for spatially modulating the phase oflight with the phase-spatial light modulator 17. The operating portion91 allows selection of any one of the plurality of modulation patterns.The controller 90 supplies information of a modulation pattern selectedby itself or by the operating portion 91 to the phase-spatial lightmodulator 17 in accordance with predetermined conditions, and thephase-spatial light modulator 17 spatially modulates the phase of light,in accordance with the modulation pattern information supplied by thecontroller 90, in the modulation pattern associated therewith inaccordance with the information.

The reflectivity of each of the half-reflecting surfaces 15 a and 19 bin the pick-up 11 is appropriately set, for example, such thatinformation light and reference light for recording incident upon theoptical information recording medium 1 have the same intensity.

FIG. 3 is a block diagram of the detection circuit 85 for detecting thefocus error signal FE, the tracking error signal TE and the reproductionsignal RF based on the output of the quadruple photodetector 29. Thedetection circuit 85 has: an adder 31 for adding the output of each ofthe diagonal light-receiving portions 29 a and 29 d of the quadruplephotodetector 29; an adder 32 for adding the output of each of thediagonal light-receiving portions 29 b and 29 c of the quadruplephotodetector 29; a subtracter 33 for calculating the difference betweenthe outputs of the adders 31 and 32 to generate the focus error signalFE based on an astigmatic method; an adder 34 for adding the output ofeach of the light-receiving portions 29 a and 29 b of the quadruplephotodetector 29 which are adjacent to each other in the direction oftracks thereof; an adder 35 for adding the output of each of thelight-receiving portions 29 c and 29 d of the quadruple photodetector 29which are adjacent to each other in the direction of the tracks thereof;a subtracter 36 for calculating the difference between the outputs ofthe adders 34 and 35 to generate the tracking error signal TE based on apush-pull method; and an adder 37 for adding the outputs of the adders34 and 35 to generate the reproduction signal RF. In the presentembodiment, the reproduction signal RF is a signal which is thereproduction of the information recorded in the address servo areas 6 ofthe optical information recording medium 1.

Servo, recording and reproducing operations of the optical informationrecording/reproducing apparatus according to the present embodiment willnow be separately described in that order. In any of the servo,recording and reproducing operations, the optical information recordingmedium 1 is rotated by the spindle motor 82 under control to maintain apredetermined rotating speed.

A servo operation will now be described with reference to FIG. 4. Duringa servo operation, all pixels of the spatial light modulator 18 are in atransmitting state. The output of the emission of light from the lightsource device 25 is set at a low output for reproduction. The controller90 predicts the timing at which light that has exited the objective lens12 passes through the address servo areas 6 based on a basic clockreproduced from a reproduction signal RF and maintains theabove-described setting while the light from the objective lens 12passes through the address servo areas 6.

Light emitted by the light source device 25 is collimated by thecollimator lens 24 to impinge upon the beam splitter 23, and a part ofthe quantity of light is transmitted by the half-reflecting surface 23 aand another part is reflected thereby. The light reflected by thehalf-reflecting surface 23 a is received by the photodetector 26. Thelight transmitted by the half-reflecting surface 23 a impinges upon theprism block 19, and a part of the quantity of light is transmitted bythe half-reflecting surface 19 b. The light transmitted by thehalf-reflecting surface 19 b passes through the spatial light modulator18 to be reflected by the reflecting surface 15 b of the prism block 15,and a part of the quantity of light is transmitted by thehalf-reflecting surface 15 a, passes through the double opticallyrotating plate 14, and is collected by the objective lens 12 to beprojected upon the optical information recording medium 1 such that itconverges at the interface between the hologram layer 3 and theprotective layer 4 of the optical information recording medium 1. Thislight is reflected by the reflecting film 5 of the optical informationrecording medium 1, modulated by embossed pits in the address servoareas 6 while being reflected, and then returned to the objective lens12.

The return light from the optical information recording medium 1 iscollimated by the objective lens 12 and passes through the doubleoptically rotating plate 14 again to impinge upon the prism block 15,and a part of the quantity of light is transmitted by thehalf-reflecting surface 15 a. The return light transmitted by thehalf-reflecting surface 15 a is reflected by the reflecting surface 15 band is transmitted by the spatial light modulator 18, and a part of thequantity of light is transmitted by the half-reflecting surface 19 b ofthe prism block 19. The return light transmitted by the half-reflectingsurface 19 b impinges upon the beam splitter 23, and a part of thequantity of light is reflected by the half-reflecting surface 23 a,passes through the convex lens 27 and cylindrical lens 28 sequentially,and is then detected by the quadruple photodetector 29. Based on theoutput of the quadruple photodetector 29, the detection circuit 85 shownin FIG. 3 generates the focus error signal FE, tracking error signal TEand reproduction signal RF based on which focus servo and tracking servois performed; the basic clock is generated; and addresses aredetermined.

In the above-described setting for servo, the pick-up 11 is configuredsimilarly to a configuration of a pick-up for recording on orreproduction from normal optical disks such as CDs (compact disks), DVDs(digital video disks or digital versatile disks) and HSs (hyper storagedisks). It is therefore possible to configure the optical informationrecording/reproducing apparatus 10 according to the present embodimentto be compatible with normal optical disk devices.

A definition will now be given to terms “A-polarized light” and“B-polarized light” which will be used in the following description. Asshown in FIG. 10, A-polarized light is linear polarized light obtainedby rotating the polarizing direction of S-polarized light at −45° or byrotating the polarizing direction of P-polarized light at +45°, andB-polarized light is linear polarized light obtained by rotating thepolarizing direction of S-polarized light at +45° or by rotating thepolarizing direction of P-polarized light at −45°. The polarizingdirections of the A-polarized light and B-polarized light are orthogonalto each other. S-polarized light is linear polarized light whosepolarizing direction is perpendicular to the plane of incidence (planeof FIG. 1), and P-polarized light is linear polarized light whosepolarizing direction is in parallel with the plane of incidence.

A recording operation will now be described. FIG. 6 is an illustrationof a state of the pick-up 11 during recording. During recording, thespatial light modulator 18 generates information light by selecting atransmitting state (hereinafter also referred to as “on”) or a blockingstate (hereinafter also referred to as “off”) for each pixel dependingon the information to be recorded to spatially modulate the light thatis passing through it. According to the present embodiment, two pixelsrepresent information of one bit, and one of two pixels associated withinformation of one bit is always on and the other is always off.

The phase-spatial light modulator 17 generates reference light forrecording having a spatially modulated phase by selectively applying aphase difference of 0 (rad) or π (rad) from a predetermined referencephase to each pixel according to a predetermined modulation pattern tospatially modulate the phase of light passing therethrough. Thecontroller 90 supplies information of a modulation pattern selected byitself or by the operating portion 91 in accordance with predeterminedconditions to the phase-spatial light modulator 17 which in turnspatially modulates the phase of light passing therethrough according tothe modulation pattern information supplied by the controller 90.

The output of light emitted by the light source device 25 is set at ahigh output to be used for recording in terms of the pulse thereof.Based on the basic clock reproduced from the reproduction signal RF, thecontroller 90 predicts timing at which light that has exited theobjective lens 12 passes through the data areas 7 and maintains theabove-described setting while the light from the objective lens 12 ispassing through the data areas 7. While the light from the objectivelens 12 is passing through the data areas 7, neither focus servo nortracking servo is performed, and the objective lens 12 is fixed. Thefollowing description is on an assumption that the light source device25 emits P-polarized light.

As shown in FIG. 6, P-polarized light emitted by the light source device25 is collimated by the collimator lens 24 to impinge upon the beamsplitter 23, and a part of the quantity of light is transmitted by thehalf-reflecting surface 23 a to impinge upon the prism block 19. A partof the light incident upon the prism block 19 is transmitted by thehalf-reflecting surface 19 b, and another part of the quantity of lightis reflected by the half-reflecting surface 19 b. The light transmittedby the half-reflecting surface 19 b passes through the spatial lightmodulator 18 in which it is spatially modulated into information lightaccording to the information to be recorded. The information light isreflected by the reflecting surface 15 b of the prism block 15, and apart of the quantity of light is transmitted by the half-reflectingsurface 15 a to pass through the double optically rotating plate 14. Thepolarizing direction of light passing through the optically rotatingplate 14L of the double optically rotating plate 14 is rotated at +45°to provide A-polarized light, and the polarizing direction of lightpassing through the optically rotating plate 14R is rotated at −45° toprovide B-polarized light. The information light having passed throughthe double optically rotating plate 14 is collected by the objectivelens 12 and is projected upon the optical information recording medium 1such that it converges on the interface between the hologram layer 3 andthe protective layer 4, i.e., on the reflecting film 5 of the opticalinformation recording medium 1.

The light reflected by the half-reflecting surface 19 b of the prismblock 19 is reflected by the reflecting surface 19 a to pass through thephase-spatial light modulator 17 in which the phase of light isspatially modulated according to a predetermined modulation pattern toprovide reference light for recording. The reference light for recordingpasses through the convex lens 16 to become convergent light. A part ofthe reference light for recording is reflected by the half-reflectingsurface 15 a of the prism block 15 to pass through the double opticallyrotating plate 14. The polarizing direction of light which has passedthrough the optically rotating plate 14L of the double opticallyrotating plate 14 is rotated at +45° to provide A-polarized light, andthe polarizing direction of light which has passed through the opticallyrotating plate 14R is rotated at −45° to provide B-polarized light. Thereference light for recording which has passed through the doubleoptically rotating plate 14 is collected by the objective lens 12 to beprojected upon the optical information recording medium 1. The lighttemporarily converges to a minimum diameter before the interface betweenthe hologram layer 3 and the protective layer 4, and thereafterdivergingly passes through the hologram layer 3.

FIGS. 7 and 8 are illustrations of states of light during recording. Inthose figures, the reference number 61 represents P-polarized light; thereference number 63 represents A-polarized light; and the referencenumber 64 represents B-polarized light.

As shown in FIG. 7, information light 51L which has passed through theoptically rotating plate 14L of the double optically rotating plate 14becomes A-polarized light which illuminates the optical informationrecording medium 1 through the objective lens 12, passes through thehologram layer 3, converges to a minimum diameter on the reflecting film5 and passes through the hologram layer 3 again after being reflected bythe reflecting film 5. Reference light 52L for recording which haspassed through the optically rotating plate 14L of the double opticallyrotating plate 14 becomes A-polarized light which illuminates theoptical information recording medium 1 through the objective lens 12,temporarily converges to a minimum diameter before the interface betweenthe hologram layer 3 and the protective layer 4 and divergingly passesthrough the hologram layer 3. Interference occurs in the hologram layer3 between the A-polarized information light 51L reflected by thereflecting film 5 and the A-polarized reference light 52L for recordingtraveling toward the reflecting film 5, so that an interference patternis formed, and the interference pattern is volumetrically recorded inthe hologram layer 3 when the light emitted by the light source device20 is at the high output.

As shown in FIG. 8, information light 51R which has passed through theoptically rotating plate 14R of the double optically rotating plate 14becomes B-polarized light which illuminates the optical informationrecording medium 1 through the objective lens 12, passes through thehologram layer 3, converges to a minimum diameter on the reflecting film5 and passes through the hologram layer 3 again after being reflected bythe reflecting film 5. Reference light 52R for recording which haspassed through the optically rotating plate 14R of the double opticallyrotating plate 14 becomes B-polarized light which illuminates theoptical information recording medium 1 through the objective lens 12,temporarily converges to a minimum diameter before the interface betweenthe hologram layer 3 and the protective layer 4 and divergingly passesthrough the hologram layer 3. Interference occurs in the hologram layer3 between the B-polarized information light 51R reflected by thereflecting film 5 and the B-polarized reference light 52R for recordingtraveling toward the reflecting film 5, so that an interference patternis formed, and the interference pattern is volumetrically recorded inthe hologram layer 3 when the light emitted by the light source device20 is at the high output.

As shown in FIGS. 7 and 8, according to the present embodiment, theinformation light and the reference light for recording illuminate thehologram layer 3 on the same side thereof such that the optical axes ofthe information light and the reference light for recording are locatedon the same line.

According to the present embodiment, phase-encoding multiplexing can beperformed to record information in the same location of the hologramlayer 3 on a multiplex basis by performing the recording operation aplurality of times in the same location of the hologram layer 3 with themodulation pattern for the reference light for recording changed.

According to the present embodiment, a reflection type (Lippmann type)hologram is thus formed in the hologram layer 3. No interference occursbetween the A-polarized information light 51L and the B-polarizedreference light 52R for recording because their polarizing directionsare orthogonal to each other and, similarly, no interference occursbetween the B-polarized information light 51R and the A-polarizedreference light 52L for recording because their polarizing directionsare orthogonal to each other. Thus, the present embodiment makes itpossible to prevent the occurrence of any unnecessary interferencefringe, thereby preventing any reduction in an SN (signal-to-noise)ratio.

According to the present embodiment, as described above, the informationlight is projected upon the optical information recording medium 1 suchthat it converges to a minimum diameter on the interface between thehologram layer 3 and the protective layer 4, and is reflected by thereflecting film 5 of the optical information recording medium 1 toreturn to the objective lens 12. The return light is incident upon thequadruple photodetector 29 in the same manner as in the servo operation.According to the present embodiment, it is therefore possible to performfocus servo also during recording utilizing the light incident upon thequadruple photodetector 29. Since the reference light for recordingconverges to a minimum diameter before the interface between thehologram layer 3 and the protective layer 4 in the optical informationrecording medium 1 to become divergent light, it forms no image on thequadruple photodetector 29 even though it is reflected by the reflectingfilm 5 of the optical information recording medium 1 to return to theobjective lens 12.

According to the present embodiment, the size of a region (hologram) inwhich one interference pattern resulting from information light andreference light is volumetrically recorded in the hologram 3 can bearbitrarily determined by moving the convex lens 16 back and forth orchanging the magnification of the same.

A reproducing operation will now be described with reference to FIG. 9.During reproduction, all pixels of the spatial light modulator 18 areon. The controller 90 supplies information of a modulation pattern forthe reference light for recording which was supplied at recording of theinformation which is now to be reproduced to the phase-spatial lightmodulator 17, and the phase-spatial light modulator 17 spatiallymodulates the phase of light passing therethrough according to themodulation pattern information supplied by the controller 90 to generatereference light for reproduction having a spatially modulated opticalphase.

The output of the light emitted by the light source device 25 is set ata low output to be used for reproduction. Based on the basic clockreproduced from the reproduction signal RF, the controller 90 predictstiming at which light that has exited the objective lens 12 passesthrough the data areas 7 and maintains the above-described setting whilethe light from the objective lens 12 is passing through the data areas7. While the light from the objective lens 12 is passing through thedata areas 7, neither focus servo nor tracking servo is performed, andthe objective lens 12 is fixed.

As shown in FIG. 9, P-polarized light emitted by the light source device25 is collimated by the collimator lens 24 to impinge upon the beamsplitter 23, and a part of the quantity of light is transmitted by thehalf-reflecting surface 23 a to impinge upon the prism block 19. A partof the light incident upon the prism block 19 is reflected by thehalf-reflecting surface 19 b. The reflected light is reflected by thereflecting surface 19 a to pass through the phase-spatial lightmodulator 17 and, at that time, the phase of the light is spatiallymodulated in a predetermined modulation pattern to provide referencelight for reproduction. The reference light for reproduction passesthrough the convex lens 16 to become convergent light. A part of thequantity of the reference light for reproduction is reflected by thehalf-reflecting surface 15 a of the prism block 15 to pass through thedouble optically rotating plate 14. The polarizing direction of lightpassing through the optically rotating plate 14L of the double opticallyrotating plate 14 is rotated at +45° to provide A-polarized light, andthe polarizing direction of light passing through the optically rotatingplate 14R is rotated at −45° to provide B-polarized light. The referencelight for reproduction that has passed through the double opticallyrotating plate 14 is collected by the objective lens 12 and is projectedupon the optical information recording medium 1. It temporarilyconverges to a minimum diameter before the interface between thehologram layer 3 and the protective layer 4, and thereafter diverginglypasses through the hologram layer 3.

FIGS. 10 and 11 are illustrations of states of light duringreproduction. The reference number 61 represents P-polarized light; thereference number 62 represents S-polarized light; the reference number63 represents A-polarized light; and the reference number 64 representsB-polarized light.

As shown in FIG. 10, reference light 53L for reproduction which haspassed through the optically rotating plate 14L of the double opticallyrotating plate 14 becomes A-polarized light which illuminates theoptical information recording medium 1 through the objective lens 12,temporarily converges to a minimum diameter before the interface betweenthe hologram layer 3 and the protective layer 4, and thereafterdivergingly passes through the hologram layer 3. As a result, thehologram layer 3 generates reproduction light 54L that is associatedwith the information light 51L for recording. The reproduction light 54Ltravels toward the objective lens 12 to be collimated by the objectivelens 12, and passes through the double optically rotating plate 14 againto become S-polarized light.

As shown in FIG. 11, reference light 53R for reproduction which haspassed through the optically rotating plate 14R of the double opticallyrotating plate 14 becomes B-polarized light which illuminates theoptical information recording medium 1 through the objective lens 12,temporarily converges to a minimum diameter before the interface betweenthe hologram layer 3 and the protective layer 4, and thereafterdivergingly passes through the hologram layer 3. As a result, thehologram layer 3 generates reproduction light 54R that is associatedwith the information light 51R for recording. The reproduction light 54Rtravels toward the objective lens 12 to be collimated by the objectivelens 12, and passes through the double optically rotating plate 14 againto become S-polarized light.

The reproduction light which has passed through the double opticallyrotating plate 14 impinges upon the prism block 15, and a part of thequantity of light is transmitted by the half-reflecting surface 15 a.The reproduction light transmitted by the half-reflecting surface 15 ais reflected by the half-reflecting surface 15 a to pass through thespatial light modulator 18, and a part of the quantity of light isreflected by the half-reflecting surface 19 b of the prism block 19 tobe incident upon and detected by the CCD array 20. A pattern originatingfrom an on/off operation of the spatial light modulator 18 duringrecording is formed on the CCD array 20, and information is reproducedby detecting this pattern.

When a plurality of pieces of information are recorded in the hologramlayer 3 on a multiplex basis by varying the modulation pattern forreference light for recording, only information associated withreference light for recording having the same modulation pattern as thatof the reference light for reproduction is reproduced among theplurality of pieces of information.

As shown in FIGS. 10 and 11, according to the present embodiment, theillumination with the reference light for reproduction and thecollection of reproduction light is carried out on the same side of thehologram layer 3 such that the optical axes of the reference light forreproduction and the reproduction light are located on the same line.

According to the present embodiment, a part of the reproduction lightimpinges upon the quadruple photodetector 29 similarly to the returnlight during the servo operation. The present embodiment therefore makesit possible to perform focus servo even during reproduction utilizingthe light incident upon the quadruple photodetector 29. Since thereference light for reproduction converges to a minimum diameter beforethe interface between the hologram layer 3 and the protective layer 4 ofthe optical information recording medium 1 to become divergent light, itforms no image on the quadruple photodetector 29 when it is reflected bythe reflecting film 5 of the optical information recording medium 1 toreturn toward the objective lens 12.

When a two-dimensional pattern of reproduction light is detected by theCCD array 20, it is required that the reproduction light and the CCDarray 20 are accurately positioned or that a reference position in thepattern of the reproduction light is recognized from data detected bythe CCD array 20. In the present embodiment, the latter is employed. Adescription will now be made with reference to FIGS. 12A, 12B, 13A and13B on a method for recognizing a reference position of a pattern ofreproduction light from data detected by the CCD array 20. As shown inFIG. 12A, the aperture of the pick-up 11 is divided by the doubleoptically rotating plate 14 into two regions 71L and 71R which aresymmetric about the optical axis thereof. Further, as shown in FIG. 12B,the aperture is divided by the spatial light modulator 18 into aplurality of pixels 72. Such a pixel 72 serves as a minimum unit oftwo-dimensional pattern data. According to the present embodiment, twopixels represent one bit of digital data “0” or “1”. One of two pixelsassociated with one bit of information is on, and the other is off. Apair of pixels which are both on or off represent error data. Thus, therepresentation of one bit of digital data with two pixels providesadvantages including an improvement in data detecting accuracy achievedby differential detection. FIG. 13A shows a pair of pixels 73 associatedwith one bit of digital data. The region where such a pair 73 exists ishereinafter referred to as “data region”. In the present embodiment,reference position information indicating a reference position in apattern of reproduction light is included in the information lightutilizing the fact that a pair of pixels which are both on or offrepresent error data. Specifically, as shown in FIG. 13B, error data areintentionally provided in a predetermined pattern in a cross-shapedregion 74 constituted by a part in parallel with the division line ofthe double optically rotating plate 14 having a width equal to twopixels and a part perpendicular to the division line having a widthequal to two pixels. This pattern of error data is hereinafter referredto as “pixel pattern for tracking”. The pixel pattern for trackingserves as the reference position information. In FIG. 13B, the referencenumber 75 represents pixels which are on, and the reference number 76represents pixels that are off. A region 77 consisting of four pixels inthe middle is always kept off.

A two-dimensional pattern as shown in FIG. 14A is obtained by combininga pixel pattern for tracking with a pattern associated with data to berecorded. In the present embodiment, regions other than the data regionsare off in the upper half of the figure and are on in the lower half,and pixels in the data regions which are contiguous with the regionsother than the data regions are in a state which is the reverse of thestate of the regions other than the data regions, i.e., they are on ifthe regions other than the data regions are off, and are off if theregions other than the data regions are on. It is therefore possible toclearly detect the boundary of data regions from data detected by theCCD array 20.

During recording, a pattern is recorded in the hologram layer 3 whichoriginates from interference between information light spatiallymodulated according to a two-dimensional pattern as shown in FIG. 14Aand reference light for recording. As shown in FIG. 14B, a pattern ofreproduction light obtained during reproduction has a contrast and an SNratio lower than those at recording. During reproduction, a pattern ofreproduction light as shown in FIG. 14B is detected by the CCD array 20to determine the data and, at this time, the data are determined byrecognizing the pixel pattern for tracking and using the position of thesame as a reference position.

FIG. 15A is a conceptual representation of contents of data determinedfrom a pattern of reproduction light. Each of regions in the figurehaving reference numbers such as A-1-1 represents one bit of data. Inthe present embodiment, a data region is divided at the cross-shapedregion 74 having a pixel pattern for tracking recorded therein into fourregions 78A, 78B, 78C and 78D. As shown in FIG. 15B, a rectangularregion is formed by combining the diagonal regions 78A and 78C; anotherrectangular region is similarly formed by combining the diagonal regions78B and 78D; and an ECC table is formed by arranging the two rectangularregions vertically. An ECC table is a table of data formed by addingerror-correcting codes (ECCs) such as CRC (cyclic redundancy check)codes to data to be recorded. FIG. 15B shows an example of an ECC tablecomprising n rows and m columns, and other arrays may be freelydesigned. The data array shown in FIG. 15A utilizes a part of the ECCtable shown in FIG. 15B, and parts of the ECC table shown in FIG. 15Bwhich are not used in the data array shown in FIG. 15A have the samevalue regardless of the contents of data. During recording, an ECC tableas shown in FIG. 15B is divided into four regions 78A, 78B, 78C and 78Das shown in FIG. 15A to be recorded in the optical information recordingmedium 1 and, during reproduction, data arranged as shown in FIG. 15Aare detected and are rearranged to reproduce an ECC table as shown inFIG. 15B, and error correction is carried out based on the ECC table toreproduce the data.

The recognition of a reference position (a pixel pattern for tracking)in a pattern of reproduction light and error correction as describedabove are performed by the signal processing circuit 89 in FIG. 2.

As described above, in the optical information recording/reproducingapparatus 10 according to the present embodiment, the illumination ofthe optical information recording medium 1 with reference light forrecording and information light during recording and the illumination ofthe optical information recording medium 1 with reference light forreproduction and the collection of reproduction light duringreproduction are all carried out on the same side of the opticalinformation recording medium 1 and on the same axis while allowingmultiplex recording of information in the optical information recordingmedium 1 utilizing phase-encoding multiplexing. This makes it possibleto configure the optical system for recording or reproduction smallerthan those in prior-art holographic recording systems and eliminates theproblem of stray light as encountered in prior-art holographic recordingsystems. The present embodiment also makes it possible to configure theoptical system for recording and reproduction in the form of the pick-up11 which is similar to normal optical disk devices. Therefore, randomaccess to the optical information recording medium 1 can be easilyperformed.

Further, according to the present embodiment, information required toperform focus servo and tracking servo can be recorded in the opticalinformation recording medium 1 to allow focus servo and tracking servoto be performed using the information. This makes it possible toposition light for recording or reproduction accurately, which resultsin improved removability, facilitates random access and allows increasesin a recording density, recording capacity and transfer rate.Particularly, the present embodiment allows dramatic increases in arecording density, recording capacity and transfer rate as a result ofthe capability of multiplex recording of information based onphase-encoding multiplexing. For example, when a series of informationis recorded in the same location of the hologram layer 3 on a multiplexbasis while changing the modulation pattern for the reference light forrecording, the information can be recorded and reproduced at a very highspeed.

The present embodiment also makes it possible to achieve copy protectionand security easily because information recorded in the opticalinformation recording medium 1 cannot be reproduced unless referencelight for reproduction is used which has the same modulation pattern asthat of the reference light for recording used to record theinformation. The present embodiment also makes it possible to provideservices e.g., a service in which a multiplicity of kinds of information(e.g., various kinds of software) with different modulation patterns forreference light are recorded in optical information recording media 1;the optical information recording media 1 themselves are provided tousers at a relatively low price; and pieces of information of thereference light modulation patterns to enable reproduction of each ofthe various kinds of information are separately sold to the users as keyinformation as requested by the users.

With the optical information recording/reproducing apparatus 10according to the present embodiment, a pattern of reproduction light canbe easily recognized because reference position information indicating areference position for the pattern of the reproduction light is includedin the information light.

The optical information recording/reproducing apparatus 10 according tothe present embodiment is compatible with conventional optical diskdevices because information recorded in the form of embossed pits in arecording medium can be reproduced by setting the pick-up 11 in theservo state shown in FIG. 4.

With the optical information recording/reproducing apparatus 10according to the present embodiment, it is quite difficult to copy anoptical information recording medium 1 having information recordedtherein because each item of information recorded in the opticalinformation recording medium 1 on a multiplex basis is associated with adifferent modulation pattern for the phase of the reference light. Thismakes it possible to prevent illegal copying.

In the optical information recording medium 1 according to the presentembodiment, since the hologram layer 3 in which information is recordedutilizing holography is separated from the layer in which information ofaddresses and the like is recorded in the form of embossed pits, thosetwo layers must be associated with each other to copy the opticalinformation recording medium 1 having information recorded therein.Copying is difficult also from this point of view, which makes itpossible to prevent illegal copying.

A description will now be made on an optical informationrecording/reproducing apparatus according to a second embodiment of thepresent invention. The present embodiment is an example in whichmultiplex recording is enabled by using phase-encoding multiplexing andhole burning type wavelength multiplexing in combination. The generalconfiguration of the optical information recording/reproducing apparatusaccording to the present embodiment is substantially the same as theconfiguration of the optical information recording/reproducing apparatus10 according to the first embodiment shown in FIG. 2.

First, hole burning type wavelength multiplexing will be brieflydescribed. Hole burning is a phenomenon in which a change in absorbanceoccurs in an absorption spectrum in the position of the wavelength ofincident light and is also referred to as “photochemical hole burning”.Hereinafter, a material that causes hole burning, i.e., a material thatcauses a change in absorbance in an absorption spectrum in the positionof the wavelength of incident light is referred to as “hole burningmaterial”. In general, a hole burning material is a material obtained bydispersing light-absorbing center materials (referred to as “guests”)such as pigment in a medium (referred to as “host”) having an irregularstructure, e.g., an amorphous structure. At extremely low temperatures,such a hole burning material exhibits a broad absorption spectrum thatis attributable to overlapping of absorption spectra of a multiplicityof guests. When such a hole burning material is illuminated with lightsuch as laser light having a certain wavelength (a wavelength within theabsorption band of the hole burning material), since only guests havinga resonance spectrum associated with the wavelength jump to a differentenergy level as a result of a photochemical reaction, a reduction ofabsorbance occurs in the absorption spectrum of the hole burningmaterial in the position of the wavelength of the illuminating light.

FIG. 16 shows a state of the absorption spectrum of a hole burningmaterial in which a reduction of absorbance has occurred in a pluralityof wavelength positions as a result of illumination with light having aplurality of wavelengths. The regions of a hole burning material where areduction of absorbance has occurred when illuminated with light arereferred to as “holes”. Since such holes are extremely small, aplurality of pieces of information with different wavelengths can berecorded on a hole burning material on a multiplex basis, and such amethod for multiplex recording is referred to as “hole burning typewavelength multiplexing”. Since the size of holes is on the order of10⁻² nm, it is assumed that multiplicity on the order of 10³ to 10⁴ canbe achieved with a hole burning material. Hole burning is described indetail, for example, in “Fundamentals of Optical Memories” published byCorona Corporation, pp. 104–133, 1990 and the above-cited article “Studyon Novel Real Time Recording and Reproduction of Wavelength MultiplexHologram Utilizing PHB”.

The present embodiment makes it possible to form a plurality ofholograms with different wavelengths on a hole burning materialutilizing hole burning type wavelength multiplexing as described above.For this purpose, a hologram layer 3 of an optical information recordingmedium 1 used in the optical information recording/reproducing apparatusaccording to the present embodiment is formed from a hole burningmaterial as described above.

According to the present embodiment, a light source device 25 in apick-up 11 is capable of selectively emitting coherent light having aplurality of wavelengths within the absorption band of the hole burningmaterial from which the hologram layer 3 is formed. The light sourcedevice 25 may be a wavelength variable laser device having a dye laserand a wavelength selecting element (a prism, diffraction grating or thelike) for selecting a wavelength of light emitted by the dye laser; awavelength variable laser device having a laser and a wavelengthselecting element utilizing a non-linear optical element for convertingthe wavelength of light emitted by the laser; or the like.

An operating portion 91 according to the present embodiment allows amodulation pattern for reference light to be selected from among aplurality of modulation patterns similarly to that in the firstembodiment and allows the wavelength of light emitted by the lightsource device 25 to be selected from among a plurality of selectablewavelengths. A controller 90 supplies information of a wavelengthselected by itself or the operating portion 91 in accordance withpredetermined conditions to the light source device 25 and, according tothe wavelength information supplied by the controller 90, the lightsource device 25 emits light having the wavelength associated therewith.The light source device 25 of the present embodiment corresponds to thewavelength selection means according to the present invention.

The configuration of the optical information recording/reproducingapparatus according to the present embodiment is otherwise the same asthat of the first embodiment.

In the optical information recording/reproducing apparatus according tothe present embodiment, when recording is performed, the wavelength oflight emitted by the light source device 25 is selected from among aplurality of selectable wavelengths. As a result, information light andreference light for recording having the selected wavelength aregenerated. According to the present embodiment, multiplex recording canbe carried out utilizing hole burning type wavelength multiplexing byperforming a recording operation a plurality of times with thewavelength of the information light and the reference light forrecording varied in the same location of the hologram layer 3.

With the optical information recording/reproducing apparatus accordingto the present embodiment, multiplex recording can be carried out whichinvolves both of phase-encoding multiplexing and hole burning typewavelength multiplexing by performing a recording operation a pluralityof times with the modulation pattern of the reference light forrecording varied at a certain wavelength in the same location of thehologram layer 3 and further performing the recording operation aplurality of times with the modulation pattern of the reference lightvaried similarly at a different wavelength. In this case, multiplicityof M×N can be achieved where N represents multiplicity achieved byphase-encoding multiplexing and M represents multiplicity achieved byhole burning type wavelength multiplexing. Therefore, the presentembodiment makes it possible to achieve greater increases in therecording density, recording capacity and transfer rate than achievablein the first embodiment.

The present embodiment makes it possible to achieve copy protection andsecurity easily like the first embodiment because information recordedin the optical information recording medium 1 cannot be reproducedunless reference light for reproduction is used which has the samewavelength as that of the information light and the reference light forrecording used to record the information. Further, when multiplexrecording is performed as a combination of phase-encoding multiplexingand hole burning type wavelength multiplexing, a higher level of copyprotection and security can be achieved because reproduction cannot beperformed unless reference light for reproduction is used which has thesame wavelength as that of the information light and the reference lightfor recording used to record the information, and which has the samemodulation pattern as that of the reference light for recording.

The present embodiment also makes it possible to provide services e.g.,a service in which a multiplicity of kinds of information (e.g., variouskinds of software) with different wavelengths of the information lightand the reference light for recording or different modulation patternsof reference light are recorded in optical information recording media1; the optical information recording media 1 themselves are provided tousers at a relatively low price; and pieces of information of thewavelengths and the modulation patterns of the reference light to enablereproduction of each of the various kinds of information are separatelysold to the users as key information as requested by the users.

The operation and effects of the present embodiment are otherwisesubstantially the same as those of the first embodiment.

An optical information recording/reproducing apparatus according to athird embodiment of the present invention will now be described. Thegeneral configuration of the optical information recording/reproducingapparatus according to the present embodiment is substantially the sameas the configuration of the optical information recording/reproducingapparatus 10 according to the first embodiment shown in FIG. 2 exceptthat the configuration of the pick-up is different from that in thefirst embodiment.

FIG. 17 is an illustration of the configuration of the pick-up accordingto the present embodiment, and FIG. 18 is a plan view of a configurationof an optical unit including various elements that form the pick-up.

The pick-up 111 according to the present embodiment has: a light sourcedevice 112 which emits coherent linearly polarized laser light; and acollimator lens 113, a neutral density filter (hereinafter referred toas “ND filter”) 114, a rotating optical element 115, a polarization beamsplitter 116, a phase-spatial light modulator 117, a beam splitter 118and a photodetector 119 which are provided in the traveling direction ofthe light emitted by the light source device 112 in the order listedthat is the order of their closeness to the light source device 112. Thelight source device 112 emits S-polarized linear light or P-polarizedlinear light. The collimator lens 113 collimates the light emitted bythe light source device 112 to emit parallel beams. The ND filter 114has the property of making the intensity distribution of the lightemitted by the collimator lens 113 uniform. The optically rotatingoptical element 115 optically rotates the light emitted by the ND filter114 to emit light including S-polarized components and P-polarizedcomponents. For example, a ½ wavelength plate or optically rotatingplate is used as the rotating optical element 115. The polarization beamsplitter 116 has a polarization beam splitter surface 116 a whichreflects the S-polarized components of the light emitted by the rotatingoptical element 115 and which transmits the P-polarized components. Thephase-spatial light modulator 117 is similar to the phase-spatial lightmodulator 17 in the first embodiment. The beam splitter 118 has a beamsplitter surface 118 a. For example, the beam splitter surface 118 atransmits 20% of the P-polarized components and reflects 80% of thesame. The photodetector 119 is used to monitor the quantity of referencelight for automatic power control (hereinafter represented by “APC”)over the reference light. A light-receiving portion of the photodetector119 may be divided into a plurality of regions to allow the adjustmentof the intensity distribution of reference light.

The pick-up 111 further has a polarization beam splitter 120, a doubleoptically rotating plate 121 and a raising mirror 122 which are providedin the traveling direction of the light emitted by the light sourcedevice 112 and reflected by the beam splitter surface 118 a of the beamsplitter 118 in the order listed that is the order of their closeness tothe beam splitter 118. The polarization beam splitter 120 has apolarization beam splitter surface 120 a for reflecting S-polarizedcomponents in light incident thereupon and for transmitting P-polarizedcomponents therein. The double optically rotating plate 121 has anoptically rotating plate 121R provided on the right side of the opticalaxis in FIG. 17 and an optically rotating plate 121L provided on theleft side of the optical axis. The optically rotating plates 121R and121L are similar to the optically rotating plates 14R and 14L of thedouble optically rotating plate 14 in the first embodiment. Theoptically rotating plate 121R optically rotates a polarizing directionat −45°, and the optically rotating plate 121L optically rotates apolarizing direction at +45°. The raising mirror 122 has a reflectingsurface which is tilted at 45° relative to the optical axis of lightfrom the double optically rotating plate 121 to reflect the light fromthe double optically rotating plate 121 in the direction perpendicularto the plane of FIG. 17.

The pick-up 111 further has: an objective lens 123 provided in thedirection in which the light from the double optically rotating plate121 travels after being reflected by the reflecting surface of theraising mirror 122 such that it faces a transparent substrate 2 of anoptical information recording medium 1 when the optical informationrecording medium 1 is secured to a spindle 81; and has an actuator 124(see FIG. 18) capable of moving the objective lens 123 in the directionof the thickness of the optical information recording medium 1 and thedirection of tracks thereof.

The pick-up 111 further has a spatial light modulator 125, a convex lens126, a beam splitter 127 and a photodetector 128 which are provided inthe traveling direction of the light emitted by the light source device112 and reflected by the polarization beam splitter surface 116 a of thepolarization beam splitter 116 in the order listed that is the order oftheir closeness to the polarization beam splitter 116. The spatial lightmodulator 125 is similar to the spatial light modulator 18 in the firstembodiment. The convex lens 126 has a function of converging informationlight before reference light for recording in the optical informationrecording medium 1 to form a region of interference between thereference light for recording and the information light. The size of theregion of interference between the reference light for recording and theinformation light can be adjusted by adjusting the position of theconvex lens 126. The beam splitter 127 has a beam splitter surface 127a. For example, the beam splitter surface 127 a transmits 20% ofS-polarized components and reflects 80% of the same. The photodetector128 is used to monitor the quantity of information light to therebyperform APC on the information light. A light-receiving portion of thephotodetector 128 may be divided into a plurality of regions to allowthe adjustment of the intensity distribution of information light. Lightthat impinges upon the beam splitter 127 from the convex lens 126 to bereflected by the beam splitter surface 127 a is incident upon thepolarization beam splitter 120.

The pick-up 111 further has a convex lens 129, a cylindrical lens 130and a quadruple photodetector 131 which are provided on the side of thebeam splitter 127 opposite to the polarization beam splitter 120 in theorder listed which is the order of their closeness to the beam splitter127. The quadruple photodetector 131 is similar to the quadruplephotodetector 29 in the first embodiment. The cylindrical lens 28 isprovided such that the center axis of a cylindrical surface thereofdefines an angle of 45° to a division line of the quadruplephotodetector 131.

The pick-up 111 further has an imaging lens 132 and a CCD array 133which are provided on the side of the beam splitter 118 opposite to thepolarization beam splitter 120 in the order listed that is the order oftheir closeness to the beam splitter 118.

The pick-up 111 further has a collimator lens 134 and a fixing lightsource device 135 which are provided on the side of the polarizationbeam splitter 116 opposite to the spatial light modulator 125 in theorder listed that is the order of their closeness to the polarizationbeam splitter 116. The fixing light source device 135 emits light forfixing information recorded in the hologram layer 3 of the opticalinformation recording medium 1, e.g., ultraviolet light having awavelength of 266 nm. A laser light source, a light source device forpassing light emitted by a laser light source through a non-linearoptical medium to emit the light with the wavelength thereof converted,or the like may be used as such a fixing light source device 135. Thecollimator lens 134 collimates light emitted by the fixing light sourcedevice 135. According to the present embodiment, the fixing light sourcedevice 135 emits S-polarized light.

As shown in FIG. 18, an optical unit 140 has an optical unit body 141.FIG. 18 shows only the region of a bottom surface of the optical unitbody 141. Attached to the optical unit body 141 are the above-describedcollimator lens 113, ND filter 114, rotating optical element 115,polarization beam splitter 116, phase-spatial light modulator 117, beamsplitter 118, polarization beam splitter 120, double optically rotatingplate 121, raising mirror 122, spatial light modulator 125, convex lens126, beam splitter 127, convex lens 129, cylindrical lens 130, imaginglens 132 and collimator lens 134.

FIG. 18 shows an example of the use of a ½ wavelength plate as therotating optical element 115. In this example, a motor 142 and a gear143 for transmitting the rotation of an output shaft of the motor 142 tothe rotating optical element 115 are provided in the optical unit body141 in order to adjust the ratio between S-polarized components andP-polarized components in light emitted by the rotating optical element115.

FIGS. 19A and 19B show an example of the rotating optical element 115 inwhich optically rotating plates are used. The rotating optical element115 in this example has two wedge-shaped optically rotating plates 115 aand 115 b that are in a face-to-face relationship with each other. Atleast either of the optically rotating plates 115 a and 115 b isdisplaced by a driving device which is not shown in the directions ofthe arrows in the figures to change the combined thickness of theoptically rotating plates 115 a and 115 b at an overlap between theoptically rotating plates 115 a and 115 b as shown in FIGS. 19A and 19B.This changes a rotating angle of light that passes through the opticallyrotating plates 115 a and 115 b, thereby changing the ratio betweenS-polarized components and P-polarized components in light emerging fromthe rotating optical element 115. A large combined thickness of theoptically rotating plates 115 a and 115 b as shown in FIG. 19A resultsin a large rotating angle, and a small combined thickness of theoptically rotating plates 115 a and 115 b as shown in FIG. 19B resultsin a small rotating angle.

The actuator 124 is mounted on a top surface of the optical unit body141. The light source device 112 is integral with a driving circuit 145for driving the light source device 112 and is mounted on a lateralsurface of the unit body 141 along with the driving circuit 145. Thephotodetector 119 is integral with an APC circuit 146 and is mounted toa lateral surface of the unit body 141 along with the APC circuit 146.The APC circuit 146 amplifies the output of the photodetector 119 togenerate a signal APC_(ref) used for APC carried out on reference light.The photodetector 128 is integral with an APC circuit 147 and is mountedto a lateral surface of the unit body 141 along with the APC circuit147. The APC circuit 147 amplifies the output of the photodetector 119to generate a signal APC_(obj) used for APC carried out on informationlight. A driving circuit 148 for driving the motor 142 is mounted to alateral surface of the unit body 141 in the vicinity of the motor 142for comparing the signals APC_(ref) and APC_(obj) from the respectiveAPC circuits 146 and 147 to optimize the ratio between S-polarizedcomponents and P-polarized components in the light emerging from therotating optical element 115.

The quadruple photodetector 131 is integral with a detection circuit 85(see FIG. 2) and is mounted to a lateral surface of the unit body 141along with the detection circuit 85. The CCD array 133 is integral witha signal processing circuit 149 for operations such as driving the CCDarray 133 and processing an output signal from the CCD array 133 and ismounted to a lateral surface of the unit body 141 along with the signalprocessing circuit 149. The fixing light source device 135 is integralwith a driving circuit 150 for driving the fixing light source device135 and is mounted to a lateral surface of the unit body 141 along withthe driving circuit 150. An input/output port 151 for input and outputof various signals between circuits in the optical unit 140 and theoutside of the optical unit 140 is further mounted to a lateral surfaceof the unit body 141. For example, an optical fiber flexible cable 152including an optical fiber for optically transmitting signals isconnected to the input/output port 151.

Although not shown, a driving circuit for driving the phase-spatiallight modulator 117 and a driving circuit for driving the spatial lightmodulator 125 are mounted on an upper surface of the optical unit body141.

FIG. 20 shows an example of a configuration of the pick-up 111 in whichthe light source device 112 is capable of transmitting laser beams inthree colors, i.e., red (hereinafter represented by “R”), green(hereinafter represented by “G”) and blue (hereinafter represented by“B”) as beams in a plurality of wavelength bands and in which the CCDarray 133 is also capable of detecting beams in the three colors R, Gand B.

The light source device 112 in the example shown in FIG. 20 has a colorsynthesis prism 161. The color synthesis prism 161 has an R-lightincidence portion 162R, a G-light incidence portion 162G and a B-lightincidence portion 162B. The incidence portions 162R, 162G and 162B areprovided with respective correction filters 163R, 163G and 163B. Thelight source device 112 further has: semiconductor laser devices(hereinafter represented by “LDs”) 164R, 164G and 164B for emitting Rlight, G light and B light respectively; and collimator lenses 165R,165G and 165B for collimating the beams of light emitted by the LDs164R, 164G and 164B and causing them to impinge upon the respectiveincidence portions 162R, 162G and 162B. The R light, G light and B lightemitted by the respective LDs 164R, 164G and 164B impinge upon the colorsynthesis prism 161 through the collimator lenses 165R, 165G and 165Band correction filters 163R, 163G and 163B to be synthesized by thecolor synthesis prism 161 and projected upon the ND filter 114. In theexample shown in FIG. 20, no collimator lens 113 as shown in FIG. 17 isprovided.

The CCD array 133 in the example shown in FIG. 20 has a color separationprism 171. The color separation prism 171 has an R-light emergingportion 172R, a G-light emerging portion 172G and a B-light emergingportion 172B. The emerging portions 172R, 172G and 172B are providedwith correction filters 173R, 173G and 173B, respectively. The CCD array133 further has CCDs 174R, 174G and 174B provided in positions in aface-to-face relationship with the respective emerging portions 172R,172G and 172B for photographing an R-light image, G-light image andB-light image. Light from the imaging lens 132 is separated by the colorseparation prism 171 into R light, G light and B light whichrespectively impinge upon the CCDs 174R, 174G and 174B through thecorrection filters 173R, 173G and 173B.

A description will now be made with reference to FIGS. 21 through 23 ona slide-feed mechanism of the optical unit 140 of the presentembodiment. FIG. 21 is a plan view of the slide-feed mechanism. FIG. 22is a partially cutaway side view of the slide-feed mechanism in astationary state. FIG. 23 is a partially cutaway side view of theslide-feed mechanism with the optical unit displaced slightly.

The slide-feed mechanism has: two shafts 181A and 181B arranged inparallel in the moving direction of the optical unit 140; two bearings182 provided on each of the shafts 181A and 181B and movable along therespective shafts 181A and 181B; a plate spring 183 for elasticallycoupling each of the bearings 182 to the optical unit 140; and a linearmotor 184 for moving the optical unit 140 along the shafts 181A and181B.

The linear motor 184 has: a coil 185 coupled to a lower end of theoptical unit 140; two yokes 186A and 186B in the form of frames providedin the moving direction of the optical unit 140 such that a part thereofpenetrates through the coil 185; and magnets 187A and 187B secured tothe inner peripheries of the yokes 186A and 186B in a face-to-facerelationship with the coil 185.

An operation of the slide-feed mechanism will now be described. When thelinear motor 184 is operated, the optical unit 140 is displaced. Whensuch a displacement is very small, as shown in FIG. 23, no displacementof the bearings 182 occurs, and the plate springs 183 between thebearings 182 and the optical unit 140 are transformed. When thedisplacement of the optical unit 140 exceeds a predetermined range, thebearings 182 are displaced to follow the optical unit 140. With such aslide-feed mechanism, no displacement of the bearings 182 occurs whenthe displacement of the optical unit 140 is very small, which makes itpossible to prevent wear of the bearings 182 attributable to sliding. Asa result, the optical unit 140 can be driven by the linear motor 184 toperform tracking servo while maintaining the durability and reliabilityof the slide-feed mechanism. A seek operation is also performed usingthe slide-feed mechanism.

The actuator 124 has a cylindrical actuator body 182 which holds theobjective lens 123 and which can be rotated about an axis 181. Theactuator body 182 is formed with two holes 183 in parallel with the axis181. A focusing coil 184 is provided at the outer periphery of theactuator body 182. Further, a coil for in-field access which is notshown is provided at a part of the outer periphery of the focusing coil184. The actuator 124 further has a magnet 185 inserted in each of theholes 183 and a magnet which is not shown provided in a face-to-facerelationship with the coil for in-field access. The objective lens 123is provided such that a line connecting the center of the objective lens123 and the axis 181 is oriented in the direction of tracks when theactuator 124 is stationary.

A description will now be made with reference to FIGS. 24A through 24Cand FIG. 27 on a method for positioning (servo) of reference light andinformation light relative to data areas of the optical informationrecording medium 1 according to the present embodiment. The actuator 124of the present embodiment is capable of moving the objective lens 123 inthe direction of the thickness of the optical information recordingmedium 1 and the direction of tracks thereof.

FIGS. 24A through 24C show the operation of moving the objective lens123 in the direction of the tracks of the optical information recordingmedium 1 with the actuator 124. The actuator 124 is in the state shownin FIG. 24B when it is stationary. When the coil for in-field accesswhich is not shown is energized, the actuator 124 changes from the stateshown in FIG. 24B to the state shown in FIG. 24A or 24C. Such anoperation of moving the objective lens 123 in the direction of thetracks of the optical information recording medium 1 is referred to as“in-field access” in the context of the present embodiment.

FIG. 25 shows a moving direction of the objective lens 123 during a seekand a moving direction of the same during in-field access. In FIG. 25,the reference number 191 represents the moving direction of theobjective lens 123 during a seek, and the reference number 192represents the moving direction of the objective lens 123 duringin-field access. The reference number 193 represents a locus of thecenter of the objective lens 123 in the case of a combination of aseeking movement and in-field access. In the case of in-field access,for example, the center of the objective lens 123 can be moved by about2 mm.

In the present embodiment, the positioning (servo) of reference lightand information light relative to the data areas of the opticalinformation recording medium 1 is carried out utilizing in-field access.FIGS. 26A and 26B are illustrations for explaining such positioning. Inthe optical information recording medium 1 according to the presentembodiment, as shown in FIG. 26A, while a groove 201 is formed on eachtrack of address servo areas 6, no groove 201 is formed in data areas 7.At the ends of an address servo area, there is formed rows of pits 202used to reproduce a clock and to indicate the end of a data area 7 itadjoins (which is referred to as “polarity” in the present embodiment).

In FIG. 26B, the reference number 203 represents a locus of the centerof the objective lens 123 during recording or reproduction. In thepresent embodiment, when multiplex recording of information is carriedout on a data area 7 using phase-encoding multiplexing or when theinformation recorded in the data area 7 on a multiplex basis isreproduced, the center of the objective lens 123 is moved using in-fieldaccess such that the center of the objective lens 123 reciprocateswithin a section including the data area 7 and a part of the addressservo areas 6 on both sides thereof as shown in FIG. 26B, instead ofstopping the center of the objective lens 123 within the data area 7.The rows of pits 202 are then used to reproduce a clock and to determinethe polarity, and the grooves 201 are used to perform focus servo andtracking servo in sections 204 in the address servo areas 6. No trackingservo is performed in a section 205 located between the sections 204including the data area 7, and the state of passage of the sections 204is maintained in this section. Turning points in the movement of thecenter of the objective lens 123 are determined to be in constantpositions based on the reproduced clock. Locations of a data area 7where information is recorded on a multiplex basis are also determinedto be in constant positions based on the reproduced clock. In FIG. 26B,the reference number 206 represents a gate signal that indicates timingfor recording or reproduction. A high (H) level of this gate signalrepresents timing for recording or reproduction. To record informationin constant locations in a data area 7 on a multiplex basis, forexample, the output of the light source device 112 may be selectivelyset at a high output for recording when the gate signal is at the highlevel. To reproduce information recorded on a multiplex basis inconstant locations of a data area 7, for example, the light sourcedevice 112 may be selectively caused to emit light when the gate signalis at the high level. In case where the CCD array 133 has the functionof an electronic shutter, images may alternatively be fetched using thefunction of an electronic shutter when the gate signal is at the highlevel.

By positioning reference light and information light according to theabove-described method, it is possible to prevent any shift of aposition of recording or reproduction even when recording orreproduction is performed for a relatively long time in the samelocation of the optical information recording medium 1. Even when theoptical information recording medium 1 is rotated, recording andreproduction can be performed as if the optical information recordingmedium 1 is stationary by performing in-field access to follow up therotation of the optical information recording medium 1, which makes itpossible to perform recording and reproduction for a relatively longtime in the same location of the optical information recording medium 1.The use of the technique of positioning reference light and informationlight utilizing in-field access as described above makes it possible toposition reference light and information light easily not only on adisk-shaped optical information recording medium 1 but also on opticalinformation recording media in other configurations such as a card-likeconfiguration.

FIG. 27 shows an example of a locus of the center of the objective lens123 in the case of access to a plurality of locations of an opticalinformation recording medium 1 utilizing a seeking movement and in-fieldaccess in combination. In the figure, a straight line in the verticaldirection represents a seek; a straight line in the horizontal directionrepresents a movement to another location in the direction of thetracks; and a region where a reciprocating motion takes place within ashort section is a region where recording or reproduction is performed.

A description will now be made with reference to FIGS. 28 and 29 on anexample of a cartridge that contains an optical information recordingmedium 1. FIG. 28 is a plan view of the cartridge, and FIG. 29 is a planview of the cartridge with a shutter thereof opened. A cartridge 211 inthis example has a window portion 212 where a part of an opticalinformation recording medium 1 contained therein is exposed and ashutter 213 for opening and closing the window portion 212. The shutter213 is urged in the direction of closing the window portion 212. Whilethe window portion 212 is normally closed as shown in FIG. 28, thecartridge 211 is moved by an optical information recording/reproducingapparatus in the direction of opening the window portion 212 as shown inFIG. 29 when it is mounted in the optical informationrecording/reproducing apparatus.

A description will now be made with reference to FIGS. 30 through 34 onexamples of arrangements of optical units 140 in cases wherein aplurality of pick-ups 111 are provided in a single optical informationrecording/reproducing apparatus.

FIG. 30 shows an example wherein two optical units 140A and 140B areprovided in a face-to-face relationship with one side of an opticalinformation recording medium 1. The optical unit 140A has aconfiguration similar to that of the optical unit 140 shown in FIG. 21(hereinafter referred to as “type A”). The optical unit 140B has aconfiguration which is in a plane symmetrical relationship with that ofthe optical unit 140 shown in FIG. 21 (hereinafter referred to as “typeB”). The two optical units 140A and 140B are provided in positions in aface-to-face relationship with the optical information recording medium1 exposed at the window portion 212 of the cartridge 211. The slide-feedmechanism of each of the optical units 140A and 140B is provided suchthat the center of an objective lens 123 of each of the optical units140A and 140B is moved along a line extending through the center of theoptical information recording medium 1.

FIG. 31 shows an example wherein two optical units are provided in aface-to-face relationship with each side of an optical informationrecording medium 1, i.e., four optical units in total are provided. FIG.32 is a sectional view taken along the line A–A′ in FIG. 31, and FIG. 33is a sectional view taken along the line B–B′ in FIG. 31. In thisexample, two optical units 140A and 140B are provided in a face-to-facerelationship with one side (back side in FIG. 31), and two optical units140C and 140D are provided in a face-to-face relationship with the otherside (top side in FIG. 31) of the optical information recording medium1. The optical unit 140C is the type A, and the optical unit 140D is thetype B.

The optical units 140A and 140B and the slide-feed mechanisms thereforand the optical units 140C and 140D and the slide-feed mechanismstherefor are arranged in accordance with the same conditions asdescribed with reference to FIG. 30. In order to effectively utilize thefour optical units 140A, 140B, 140C and 140D, an optical informationrecording medium 1 must be used which allows recording and reproductionof information on both sides thereof.

FIG. 34 shows an example wherein eight optical units are provided in aface-to-face relationship with each side of an optical informationrecording medium 1, i.e., sixteen optical units are provided in total.In this example, eight optical units 140 ₁ through 140 ₈ are provided ina face-to-face relationship with one side (top side in FIG. 34), andeight optical units 140 ₉ through 140 ₁₆ are provided in a face-to-facerelationship with the other side (back side in FIG. 34) of the opticalinformation recording medium 1. The optical units 140 ₁, 140 ₃, 140 ₅,140 ₇, 140 ₁₀, 140 ₁₂, 140 ₁₄ and 140 ₁₆ are the type A. The opticalunits 140 ₂, 140 ₄, 140 ₆, 140 ₈, 140 ₉, 140 ₁₁, 140 ₁₃, and 140 ₁₅, arethe type B. The slide-feed mechanism of each of the optical units isprovided such that the center of the objective lens 123 of each opticalunit is moved along a line extending through the center of the opticalinformation recording medium 1. In order to effectively utilize thesixteen optical units, an optical information recording medium 1 must beused which is not contained in a cartridge and which allows recordingand reproduction of information on both sides thereof.

In a system including the optical information recording/reproducingapparatus and the optical information recording medium 1 according tothe present embodiment, an extraordinary amount of information can berecorded in the optical information recording medium 1, and such asystem is suitable for applications in which an enormous amount ofcontinuous information is recorded. If a system used for such anapplication is unable to reproduce information during recording of suchan enormous amount of continuous information, the system will be verymuch difficult to use.

Under such circumstances, for example, a plurality of pick-ups 111 maybe provided in a single optical information recording/reproducingapparatus as shown in FIGS. 30 through 34 to allow simultaneousrecording and reproduction of information using a single opticalinformation recording medium 1 and to allow simultaneous recording andreproduction of information with the plurality of pick-ups 111, whichmakes it possible to improve the recording and reproducing performanceand, particularly, to configure a system which is easy to use even inapplications wherein an enormous amount of continuous information isrecorded. By providing a plurality of pick-ups 111 in a single opticalinformation recording/reproducing apparatus, dramatic improvement ofperformance can be achieved in retrieving a desired item of informationfrom a large amount of information compared to a case in which only asingle pick-up 111 is used.

A description will now be made with reference to FIGS. 35 through 46 onan example of a specific structure of an optical information recordingmedium 1 according to the present embodiment.

The optical information recording medium 1 according to the presentembodiment has a first information layer (hologram layer) in whichinformation is recorded utilizing holography and a second informationlayer in which information for servo and address information arerecorded in the form of embossed pits or the like. It is necessary toform a region of interference between reference light for recording andinformation light to a certain size in the first information layer whileconverging the reference light to a minimum diameter in the secondinformation layer. For this reason, according to the present embodiment,a gap having a certain size is formed between the first and secondinformation layers. This makes it possible to form a region ofinterference between reference light for recording and information lightwith a sufficient size in the first layer while converging the referencelight to a minimum diameter on the second information layer to allowreproduction of information recorded in the second information layer.Optical information recording media 1 according to the presentembodiment can be classified into an air gap type and a transparentsubstrate gap type depending on the method for forming such a gap.

FIGS. 35 through 37 show an air gap type optical information recordingmedium 1 wherein FIG. 35 is a sectional view of one half of the opticalinformation recording medium 1; FIG. 36 is an exploded perspective viewof the one half of the optical information recording medium 1; and FIG.37 is a perspective view of the one half of the optical informationrecording medium 1. The optical information recording medium 1 has: areflecting substrate 221 one surface of which is a reflecting surface; atransparent substrate 222 provided in a face-to-face relationship withthe reflecting surface of the reflecting substrate 221; an outercircumferential spacer 223 and an inner circumferential spacer 224 forspacing the reflecting substrate 221 and transparent substrate 222 witha predetermined gap therebetween; and a hologram layer 225 bonded to thesurface of the transparent substrate 222 facing the reflecting substrate221. An air gap having a predetermined thickness is formed between thereflecting surface of the reflecting substrate 221 and the hologramlayer 225. The hologram layer 225 serves as the first information layer.Pre-grooves are formed on the reflecting surface of the reflectingsubstrate 221, and the reflecting surface serves as the secondinformation layer.

FIGS. 38 through 40 show a transparent substrate type opticalinformation recording medium 1 wherein FIG. 38 is a sectional view ofone half of the optical information recording medium 1; FIG. 39 is anexploded perspective view of the one half of the optical informationrecording medium 1; and FIG. 40 is a perspective view of the one half ofthe optical information recording medium 1. The optical informationrecording medium 1 is configured by stacking a transparent substrate231, a hologram layer 232 to serve as the first information layer and atransparent substrate 233 in the order listed. Pre-grooves are formedand a reflecting film 234 is provided on the surface of the transparentsubstrate 231 opposite to the hologram layer 232. The surface of thetransparent substrate 231 opposite to the hologram layer 232 serves asthe second information layer. A gap having a predetermined thickness isformed by the transparent substrate 231 between the second informationlayer and the hologram layer 232. The thickness of the transparentsubstrate 233 is smaller than that of the transparent substrate 231.

Optical information recording media 1 according to the presentembodiment can be classified into a single-sided type and a double-sidedtype.

FIGS. 41 through 43 show single-sided type optical information recordingmedia 1 wherein FIG. 41 is a sectional view of a 1.2 mm thickness typeoptical information recording medium 1; FIG. 42 is a sectional view of a0.6 mm thickness type optical information recording medium 1; and FIG.43 is an illustration of how to illuminate a single-sided opticalinformation recording medium 1 with reference light for recording andinformation light. The optical information recording media 1 shown inFIGS. 41 and 42 have a structure as shown in FIG. 38. The combinedthickness of the transparent substrate 231, hologram layer 232 andtransparent substrate 233 of the optical information recording medium 1shown in FIG. 41 is 1.2 mm, and the combined thickness of thetransparent substrate 231, hologram layer 232 and transparent substrate233 of the optical information recording medium 1 shown in FIG. 42 is0.6 mm.

Reference light 241 for recording projected upon the optical informationrecording medium 1 by the objective lens 123 converges to a minimumdiameter on the surface having pre-grooves formed thereon, andinformation light 242 projected upon the optical information recordingmedium 1 by the objective lens 123 converges to a minimum diameterbefore the hologram layer 232. As a result, a region 243 of interferencebetween the reference light 241 for recording and the information light242 is formed in the hologram layer 232.

While FIGS. 41 and 42 show optical information recording media 1belonging to the transparent substrate gap type and the single-sidedtype, an optical information recording medium 1 may be configured whichbelongs to the air-gap type and the single-sided type. In such a case,the combined thickness of the transparent substrate 222, hologram layer225 and the air gap must be 1.2 mm or 0.6 mm.

FIGS. 44 through 46 show double-sided type optical information recordingmedia 1 wherein FIG. 44 is a sectional view of a transparent substrategap type optical information recording medium 1; FIG. 45 is a sectionalview of an air gap type optical information recording medium 1; and FIG.46 is an illustration of how to illuminate a double-sided opticalinformation recording medium 1 with reference light for recording andinformation light. The optical information recording medium 1 shown inFIG. 44 has a structure formed of two single-sided type opticalinformation recording media as shown in FIG. 42 which are laminated toeach other at the reflecting films 234 thereof. The optical informationrecording medium 1 shown in FIG. 45 has a structure formed of twosingle-sided type optical information recording media as shown in FIG.35 which are laminated to each other at the reflecting substrates 221thereof. The combined thickness of the transparent substrate 222,hologram layer 225 and the air gap of one side of the opticalinformation recording medium 1 shown in FIG. 45 is 0.6 mm.

Reference light 241 for recording projected upon the optical informationrecording medium 1 by the objective lens 123 converges to a minimumdiameter on the surface having pre-grooves formed thereon, andinformation light 242 projected upon the optical information recordingmedium 1 by the objective lens 123 converges to a minimum diameterbefore the hologram layers 232 and 225. As a result, a region 243 ofinterference between the reference light 241 for recording and theinformation light 242 is formed in the hologram layers 232 and 225.

The optical information recording/reproducing apparatus of the presentembodiment is capable of recording and reproducing information usingconventional optical disks. For example, when a single-sided typeoptical disk 251 is used which has pre-grooves formed on one side of atransparent substrate 252 thereof and which is provided with areflecting film 253 as shown in FIG. 47, light projected upon theoptical disk 251 by the objective lens 123 is converged to a minimumdiameter on the surface of the optical disk 251 formed with pre-grooves,i.e., an information layer, as shown in FIG. 48. For example, thethickness of the transparent substrate 252 of the optical disk 251 shownin FIG. 47 is 1.2 mm. Optical disks having a structure as shown in FIG.47 include CDs, CD-ROMs, CD-Rs (write once type CDs) and MDs(mini-disks).

When a double-sided type optical disk 261 is used which has a structureformed by two transparent substrates 262 formed with pre-grooves andprovided with a reflecting film 263 on one side thereof which arelaminated to each other at the reflecting films 263 as shown in FIG. 49,light projected upon the optical disk 261 by the objective lens 123 isconverged to a minimum diameter on the surface of the optical disk 261formed with pre-grooves, i.e., an information layer, as shown in FIG.50. For example, the thickness of one of the transparent substrates 262of the optical disk 261 shown in FIG. 49 is 0.6 mm. Optical disks havinga structure as shown in FIG. 50 include DVDs, DVD-ROMs, DVD-RAMs, MOs(magneto-optical disks).

The second information layer of the optical information recording medium1 according to the present embodiment may be similar in configuration toinformation layers of conventional optical disks, for example, as shownin FIGS. 47 and 49, including the contents of information recordedtherein. In this case; information recorded in the second informationlayer can be reproduced by putting the pick-up 111 in a servo state.Since information for servo and address information are recorded in theinformation layer of a conventional optical disk, by configuring thesecond information layer similarly to the information layer of aconventional optical disk, information for servo and address informationrecorded in the information layer of a conventional optical disk can beused, as it is, to position information light, reference light forrecording and reference light for reproduction in the hologram layer forperforming recording and reproduction. The second information layerserves a wide range of applications, e.g., high speed retrieval can beperformed by recording directory information, directory managementinformation and the like for information recorded in the firstinformation layer (hologram layer) in the second information layer(information layer of a conventional optical disk).

Prior to a description of the operation of the optical informationrecording/reproducing apparatus according to the present embodiment, adescription will now be made on a principle behind phase-encodingmultiplexing with reference to FIG. 51 and FIGS. 52A through 52C. FIG.51 is a perspective view showing a schematic configuration of a commonrecording/reproducing system for performing phase-encoding multiplexing.The recording/reproducing system has: a spatial light modulator 301 forgenerating information light 302 based on two-dimensional digitalpattern information; a lens 303 for collecting the information light 302from the spatial light modulator 301 to illuminate a hologram recordingmedium 300 with the same; a phase-spatial light modulator 304 forgenerating reference light 305 having a spatially modulated phase toilluminate the hologram recording medium 300 with the reference light305 in a direction substantially orthogonal to the information light302; a CCD array 308 for detecting reproduced two-dimensional digitalpattern information; and a lens 307 for collecting reproduction light306 emitted by the hologram recording medium 300 and for projecting thesame upon the CCD array 308.

During recording, the recording/reproducing system shown in FIG. 51digitizes information such as an original image to be recorded andrearranges resultant signals having a value of 0 or 1 on atwo-dimensional basis to generate two-dimensional digital patterninformation (hereinafter referred to as “page data”). Let us assume herethat page data #1 through #n are recorded in the same hologram recordingmedium 300 on a multiplex basis. Further, different items oftwo-dimensional digital pattern information #1 through #n for phasemodulation (hereinafter referred to as “phase data”) are generated forthe respective page data #1 through #n. First, when the page data #1 isrecorded, the spatial light modulator 301 generates spatially modulatedinformation light 302 based on the page data #1 to illuminate thehologram recording medium 300 through the lens 303. Simultaneously, thephase-spatial light modulator 304 generates reference light 305 having aspatially modulated phase based on the phase data #1 to illuminate thehologram recording medium 300. As a result, interference fringesresulting from overlap between the information light 302 and thereference light 305 are recorded in the hologram recording medium 300.Similarly, to record the page data #2 through #n, the spatial lightmodulator 301 generates spatially modulated information light 302 basedon the page data #2 through #n; the phase-spatial light modulator 304generates reference light 305 having a spatially modulated phase basedon the phase data #2 through #n; and the hologram recording medium 300is illuminated with the information light 302 and the reference light305. Thus, a plurality of pieces of information are recorded in the samelocation of the hologram recording medium 300 on a multiplex basis. Sucha hologram having information recorded therein on a multiplex basis isreferred to as “stack”. In the example shown in FIG. 51, the hologramrecording medium 300 has a plurality of stacks (stack 1, stack 2, . . ., stack m, . . . ).

Arbitrary page data can be reproduced from a stack by illuminating thestack with the reference light 305 having a phase which has beenspatially modulated based on the same phase data as used for therecording of the page data. As a result, the reference light 305 isselectively diffracted by interference fringes associated with the phasedata and page data to produce reproduction light 306. The reproductionlight 306 impinges upon the CCD array 308 through the lens 307, and theCCD array 308 detects a two-dimensional pattern of the reproductionlight. The detected two-dimensional pattern of the reproduction light isdecoded conversely to the process for recording, so that the informationsuch as an original image is reproduced.

FIGS. 52A through 52C show how interference fringes are formed in thehologram recording medium 300 as a result of interference betweeninformation light 302 and reference light 305. FIG. 52A shows howinterference fringes 309 ₁ are formed as a result of interferencebetween information light 302 ₁ based on the page data #1 and referencelight 305 ₁ based on the phase data #1. Similarly, FIG. 52B shows howinterference fringes 309 ₂ are formed as a result of interferencebetween information light 302 ₂ based on the page data #2 and referencelight 305 ₂ based on the phase data #2. FIG. 52C shows how interferencefringes 309 ₃ are formed as a result of interference between informationlight 302 ₃ based on the page data #3 and reference light 305 ₃ based onthe phase data #3.

Servo, recording and reproducing operations of the optical informationrecording/reproducing apparatus according to the present embodiment willnow be separately described in that order.

A servo operation will now be described with reference to FIGS. 53 and54. FIG. 53 is an illustration of a state of the pick-up 111 during aservo operation. During a servo operation, all pixels of the spatiallight modulator 125 are in a blocking state. The phase-spatial lightmodulator 117 is set such that light passing through all pixels have thesame phase. The output of the emission of light from the light sourcedevice 112 is set at a low output for reproduction. The controller 90predicts the timing at which light that has exited the objective lens123 passes through the address servo areas 6 based on a basic clockreproduced from a reproduction signal RF and maintains theabove-described setting while the light from the objective lens 123passes through the address servo areas 6.

Light emitted by the light source device 112 is collimated by thecollimator lens 113 to impinge upon the polarization beam splitter 116after passing through the ND filter 114 and rotating optical element 115sequentially. S-polarized components in the light incident upon thepolarization beam splitter 116 are reflected by the polarization beamsplitter surface 116 a and are blocked by the spatial light modulator125. P-polarized components in the light incident upon the polarizationbeam splitter 116 are transmitted by the polarization beam splittersurface 116 a and passes through the phase-spatial light modulator 117to impinge upon the beam splitter 118. A part of the light incident uponthe beam splitter 118 is reflected by the beam splitter surface 118 aand passes through the polarization beam splitter 120 to impinge uponthe double optically rotating plate 121. Light that has passed throughthe optically rotating plate 121R of the double optically rotating plate121 becomes B-polarized light, and light that has passed through theoptically rotating plate 121L becomes A-polarized light. The light thathas passed through the double optically rotating plate 121 is reflectedby the raising mirror 122, collected by the objective lens 123 andprojected upon the optical information recording medium 1 so that itconverges on the pre-grooves of the optical information recording medium1 located further than the hologram layer. This light is reflected onthe pre-grooves and, at that time, it is modulated by pits formed on thepre-grooves and then returns to the objective lens 123. The raisingmirror 122 is omitted in FIG. 53.

The return light from the optical information recording medium 1 iscollimated by the objective lens 123 and passes through the doubleoptically rotating plate 121 to become S-polarized light. The returnlight is reflected by the polarization beam splitter surface 120 a ofthe polarization beam splitter 120 to impinge upon the beam splitter127. A part of the light is transmitted by the beam splitter surface 127a and passes through the convex lens 129 and cylindrical lens 130sequentially to be detected by the quadruple photodetector 131. Based onthe output of the quadruple photodetector 131, the detection circuit 85generates a focus error signal FE, tracking error signal TE andreproduction signal RF based on which focus servo and tracking servo areperformed; the basic clock is generated; and addresses are determined.

A part of the light incident upon the beam splitter 118 impinges uponthe photodetector 119, and a signal APC_(ref) is generated by the APCcircuit 146 based on a signal output by the photodetector 119. APC isperformed based on the signal APC_(ref) such that the opticalinformation recording medium 1 is illuminated with a constant quantityof light. Specifically, the driving circuit 148 drives the motor 142 toadjust the rotating optical element 115 such that the signal APC_(ref)equals a predetermined value. Alternatively, during the servo operation,APC may be performed by setting the rotating optical element 115 andadjusting the output of the light source device 112 such that lightwhich has passed through the rotating optical element 115 hasP-polarized components only. When the light-receiving portion of thephotodetector 119 is divided into a plurality of regions and thephase-spatial light modulator 117 is capable of adjusting the quantityof light transmitted thereby, the quantity of light transmitted by eachpixel of the phase-spatial light modulator 117 may be adjusted based ona signal output by each of the light-receiving portions of thephotodetector 119 to adjust the light projected upon the opticalinformation recording medium 1 so as to achieve a uniform intensitydistribution.

In the above-described setting for a servo operation, the configurationof the pick-up 111 is similar to the configuration of a pick-up forrecording and reproduction on a normal optical disk. Therefore, theoptical information recording/reproducing apparatus according to thepresent embodiment is capable of recording and reproducing by using anormal optical disk.

FIG. 54 is an illustration of a state of light in the vicinity of anoptical disk in the case of recording and reproduction using a normaloptical disk with the optical information recording/reproducingapparatus according to the present embodiment. A double-sided typeoptical disk 261 is illustrated here as an example of a normal opticaldisk. In the optical disk 261, pre-grooves 265 are formed on the sidesof transparent substrates 262 where reflecting films 263 are provided,and light from the objective lens 123 is projected upon the optical disk261 such that it converges on the pre-grooves 265 and is returned to theobjective lens 123 after being modulated by pits formed on thepre-grooves 265.

A recording operation will now be described with reference to FIGS. 55through 57. FIG. 55 is an illustration of a state of the pick-up 111during recording, and each of FIGS. 56 and 57 is an illustration of astate of light in the vicinity of the optical information recordingmedium 1 during recording. The following description will refer to theuse of an air gap type optical information recording medium 1 as anexample, as shown in FIG. 56.

During recording, the spatial light modulator 125 generates informationlight by selecting a transmitting state (hereinafter also referred to as“on”) or a blocking state (hereinafter also referred to as “off”) foreach pixel depending on the information to be recorded to modulate thelight that is passing through it. The phase-spatial light modulator 117generates reference light for recording having a spatially modulatedoptical phase by selectively applying a phase difference of 0 (rad) or π(rad) from a predetermined reference phase to each pixel according to apredetermined modulation pattern to modulate the phase of light passingtherethrough.

According to the present embodiment, as already described, whenmultiplex recording of information is carried out on a data area 7 usingphase-encoding multiplexing, the center of the objective lens 123 ismoved using in-field access such that the center of the objective lens123 reciprocates within a section including the data area 7 and a partof the address servo areas 6 on both sides thereof. When the center ofthe objective lens 123 has come to a predetermined position in the dataarea 7, the output of the light source device 112 is selectively set ata high output for recording.

Light emitted by the light source device 112 is collimated by thecollimator lens 113 to impinge upon the polarization beam splitter 116after passing through the ND filter 114 and rotating optical element 115sequentially. P-polarized components in the light incident upon thepolarization beam splitter 116 are transmitted by the polarization beamsplitter surface 116 a to pass through the phase-spatial light modulator117 and, at that time, the phase of the light is spatially modulated toprovide reference light for recording. The reference light for recordingimpinges upon the beam splitter 118. A part of the reference light forrecording incident upon the beam splitter 118 is reflected by the beamsplitter surface 118 a and passes through the polarization beam splitter120 to impinge upon the double optically rotating plate 121. Referencelight for recording that has passed through the optically rotating plate121R of the double optically rotating plate 121 becomes B-polarizedlight, and reference light for recording that has passed through theoptically rotating plate 121L becomes A-polarized light. The referencelight for recording that has passed through the double opticallyrotating plate 121 is reflected by the raising mirror 122, collected bythe objective lens 123 and projected upon the optical informationrecording medium 1 so that it converges beyond the hologram layer 225 ofthe optical information recording medium 1. The raising mirror 122 isomitted in FIG. 55.

S-polarized components in the light incident upon the polarization beamsplitter 116 are reflected by the polarization beam splitter surface 116a to pass through the spatial light modulator 125 and, at that time, thelight is spatially modulated according to the information to be recordedto provide information light. The information light impinges upon thebeam splitter 127. A part of the information light incident upon thebeam splitter 127 is reflected by the beam splitter surface 127 a and isreflected by the beam splitter surface 120 a of the polarization beamsplitter 120 to impinge upon the double optically rotating plate 121.Information light that has passed through the optically rotating plate121R of the double optically rotating plate 121 becomes A-polarizedlight, and information light that has passed through the opticallyrotating plate 121L becomes B-polarized light. The information lightthat has passed through the double optically rotating plate 121 isreflected by the raising mirror 122, collected by the objective lens 123and projected upon the optical information recording medium 1 so that ittemporarily converges before the hologram layer 225 of the opticalinformation recording medium 1 and then divergingly passes through thehologram layer 225.

As a result, a region 313 of interference between reference light 311for recording and information light 312 is formed in the hologram layer225, as shown in FIG. 56. The interference region 313 is in the form ofa barrel. As shown in FIG. 55, the converging position of theinformation light can be adjusted by adjusting the position 310 of theconvex lens 126, which makes it possible to adjust the size of theinterference region 313.

In the hologram layer 225, as shown in FIG. 57, interference occursbetween A-polarized reference light 311A for recording that has passedthrough the optically rotating plate 121L of the double opticallyrotating plate 121 and A-polarized information light 312A that haspassed through the optically rotating plate 121R of the double opticallyrotating plate 121; and interference occurs between B-polarizedreference light 311B for recording that has passed through the opticallyrotating plate 121R of the double optically rotating plate 121 andB-polarized information light 312B that has passed through the opticallyrotating plate 121L of the double optically rotating plate 121,resultant interference patterns being volumetrically recorded in thehologram layer 225.

By changing the modulation pattern for the phase of the reference lightfor recording for each item of information to be recorded, a pluralityof pieces of information can be recorded in the same location of thehologram layer 225 on a multiplex basis.

As shown in FIG. 55, a part of the reference light for recordingincident upon the beam splitter 118 impinges upon the photodetector 119,and a signal APC_(ref) is generated by the APC circuit 146 based on asignal output by the photodetector 119. A part of the information lightincident upon the beam splitter 127 impinges upon the photodetector 128,and a signal APC_(obj) is generated by the APC circuit 147 based on asignal output by the photodetector 128. Based on the signals APC_(ref)and APC_(obj), APC is performed such that the ratio between theintensity of the reference light for recording and the information lightilluminating the optical information recording medium 1 is set at anoptimum value. Specifically, the driving circuit 148 compares thesignals APC_(ref) and APC_(obj) and drives the motor 142 to adjust therotating optical element 115 such that the signals are in a desiredratio. When the light-receiving portion of the photodetector 119 isdivided into a plurality of regions and the phase-spatial lightmodulator 117 is capable of adjusting the quantity of light transmittedthereby, the quantity of light transmitted by each pixel of thephase-spatial light modulator 117 may be adjusted based on a signaloutput by each of the light-receiving portions of the photodetector 119to adjust the light projected upon the optical information recordingmedium 1 so as to achieve a uniform intensity distribution. Similarly,when the light-receiving portion of the photodetector 128 is dividedinto a plurality of regions and the spatial light modulator 125 is alsocapable of adjusting the quantity of light transmitted thereby, thequantity of light transmitted by each pixel of the spatial lightmodulator 125 may be adjusted based on a signal output by each of thelight-receiving portions of the photodetector 128 to adjust the lightprojected upon the optical information recording medium 1 so as toachieve a uniform intensity distribution.

According to the present embodiment, APC is carried out based on the sumof the signals APC_(ref) and APC_(obj) such that the total intensity ofthe reference light for recording and the information light becomes anoptimum value. Methods for controlling the total intensity of thereference light for recording and the information light include controlover a peak value of the output of the light source device 112 andcontrol over an emission pulse width and a profile of the intensity ofemitted light over time when light is emitted in the form of pulses.

A fixing operation will now be described with reference to FIGS. 58 and59. FIG. 58 is an illustration of a state of the pick-up 111 during afixing operation, and FIG. 59 is an illustration of a state of light inthe vicinity of the optical information recording medium 1 duringfixing. During a fixing operation, all pixels of the spatial lightmodulator 125 are in a blocking state. The phase-spatial light modulator117 is set such that light passing through all pixels thereof have thesame phase. No light is emitted by the light source device 112, andS-polarized ultraviolet light for fixing is emitted by the fixing lightsource device 135.

Light emitted by the fixing light source device 135 is collimated by thecollimator lens 134 to impinge upon the polarization beam splitter 116,reflected by the polarization beam splitter surface 116 a and passesthrough the phase-spatial light modulator 117 to impinge upon the beamsplitter 118. A part of the light incident upon the beam splitter 118 isreflected by the beam splitter surface 118 a to impinge upon the doubleoptically rotating plate 121 through the polarization beam splitter 120.Light that has passed through the optically rotating plate 121R of thedouble optically rotating plate 121 becomes B-polarized light, and lightthat has passed through the optically rotating plate 121L becomesA-polarized light. The light that has passed through the doubleoptically rotating plate 121 is reflected by the raising mirror 122,collected by the objective lens 123 and projected upon the opticalinformation recording medium 1 so that it converges on the pre-groovesof the optical information recording medium 1 located further than thehologram layer 225. This light fixes the interference pattern formed inthe interference region 313 in the hologram layer 225. The raisingmirror 122 is omitted in FIG. 58.

The positioning (servo) of fixing light on an optical informationrecording medium 1 can be performed similarly to the positioning ofreference light for recording and information light during recording.

A part of the light incident upon the beam splitter 118 impinges uponthe photodetector 119, and a signal APC_(ref) is generated by the APCcircuit 146 based on a signal output by the photodetector 119. Based onthe signal APC_(ref), APC is performed such that the quantity of fixinglight illuminating the optical information recording medium 1 isconstant. Specifically, the output of the fixing light source device 135is adjusted such that the signal APC_(ref) equals a predetermined value.Alternatively, when the light-receiving portion of the photodetector 119is divided into a plurality of regions and the phase-spatial lightmodulator 117 is capable of adjusting the quantity of light transmittedthereby, the fixing light illuminating the optical information recordingmedium 1 may be adjusted to achieve a uniform intensity of light byadjusting the quantity of light transmitted by each of the pixels of thephase-spatial light modulator 117 based on a signal output by each ofthe light-receiving portions of the photodetector 119.

A reproducing operation will now be described with reference to FIGS. 60through 62. FIG. 60 is an illustration of a state of the pick-up 111during reproduction, and each of FIGS. 61 and 62 is an illustration of astate of light in the vicinity of an optical information recordingmedium 1 during reproduction.

During reproduction, all pixels of the spatial light modulator 125 arein a blocking state. The phase-spatial light modulator 117 generatesreference light for reproduction having a spatially modulated opticalphase by selectively applying a phase difference of 0 (rad) or π (rad)from a predetermined reference phase to each pixel according to apredetermined modulation pattern to modulate the phase of light passingtherethrough. According to the present embodiment, a modulation patternfor the phase of reference light for reproduction is a pattern which isin a point symmetrical relationship with a modulation pattern of thephase of reference light for recording at the time of recording of theinformation to be reproduced about the center of the phase-spatial lightmodulator 117.

Light emitted by the light source device 112 is collimated by thecollimator lens 113 to impinge upon the polarization beam splitter 116after passing through the ND filter 114 and the rotating optical element115 sequentially. S-polarized components in the light incident upon thepolarization beam splitter 116 are reflected by the polarization beamsplitter surface 116 a and are blocked by the spatial light modulator125. P-polarized components in the light incident upon the polarizationbeam splitter 116 are transmitted by the polarization beam splittersurface 116 a to pass through the phase-spatial light modulator 117 and,at that time, the phase of the light is spatially modulated to providereference light for reproduction. The reference light for reproductionimpinges upon the beam splitter 118. A part of the reference light forreproduction incident upon the beam splitter 118 is reflected by thebeam splitter surface 118 a and passes through the polarization beamsplitter 120 to impinge upon the double optically rotating plate 121.Reference light for reproduction that has passed through the opticallyrotating plate 121R of the double optically rotating plate 121 becomesB-polarized light, and reference light for reproduction that has passedthrough the optically rotating plate 121L becomes A-polarized light. Thereference light for reproduction that has passed through the doubleoptically rotating plate 121 is reflected by the raising mirror 122,collected by the objective lens 123 and projected upon the opticalinformation recording medium 1 so that it converges beyond the hologramlayer 225 of the optical information recording medium 1. The raisingmirror 122 is omitted in FIG. 60.

The positioning (servo) of reference light for reproduction on anoptical information recording medium 1 can be performed similarly to thepositioning of reference light for recording and information lightduring recording.

As shown in FIG. 62, B-polarized reference light 315B for reproductionthat has passed through the optically rotating plate 121R of the doubleoptically rotating plate 121 passes through the hologram layer 225, andis reflected by the reflecting surface located at a converging positionon the further side of the hologram layer 225, and then passes throughthe hologram layer 225 again. At this time, the reference light 315B forreproduction reflected by the reflecting surface passes through thelocation in the interference region 313 that was illuminated with thereference light 311A for recording during recording, and has the samemodulation pattern as that of the reference light 311A for recording.Therefore, the reference light 315B for reproduction results in theemission of reproduction light 316B associated with the informationlight 312A at the time of recording from the interference region 313.The reproduction light 316B travels toward the objective lens 123.

Similarly, A-polarized reference light 315A for reproduction that haspassed through the optically rotating plate 121L of the double opticallyrotating plate 121 passes through the hologram layer 225, and isreflected by the reflecting surface located at the converging positionon the further side of the hologram layer 225, and then passes throughthe hologram layer 225 again. At this time, the reference light 315A forreproduction reflected by the reflecting surface passes through thelocation in the interference region 313 that was illuminated with thereference light 311B for recording during recording, and has the samemodulation pattern as that of the reference light 311B for recording.Therefore, the reference light 315A for reproduction results in theemission of reproduction light 316A associated with the informationlight 312B at the time of recording from the interference region 313.The reproduction light 316A travels toward the objective lens 123.

After passing through the objective lens 123, the B-polarizedreproduction light 316B passes through the optically rotating plate 121Rof the double optically rotating plate 121 to become P-polarized light.After passing through the objective lens 123, the A-polarizedreproduction light 316A passes through the optically rotating plate 121Lof the double optically rotating plate 121 to become P-polarized light.The reproduction light that has passed through the double opticallyrotating plate 121 impinges upon the polarization beam splitter 120 andis transmitted by the polarization beam splitter surface 120 a toimpinge upon the beam splitter 118. A part of the reproduction lightincident upon the beam splitter 118 is transmitted by the beam splittersurface 118 a and passes through the imaging lens 132 to impinge uponthe CCD array 133. As shown in FIG. 60, the state of imaging of thereproduction light on the CCD array 133 can be adjusted by adjusting theposition of the imaging lens 132.

A pattern originating from an on/off operation of the spatial lightmodulator 125 during recording is formed on the CCD array 133, andinformation is reproduced by detecting this pattern. When a plurality ofpieces of information are recorded in the hologram layer 225 on amultiplex basis by varying the modulation pattern for reference lightfor recording, only information associated with reference light forrecording having a modulation pattern in a point symmetricalrelationship with the modulation pattern of the reference light forreproduction is reproduced among the plurality of pieces of information.

A part of the reference light for reproduction incident upon the beamsplitter 118 impinges upon the photodetector 119, and a signal APC_(ref)is generated by the APC circuit 146 based on a signal output by thephotodetector 119. Based on the signal APC_(ref), APC is performed suchthat the optical information recording medium 1 is illuminated with aconstant quantity of light. Specifically, the driving circuit 148 drivesthe motor 142 to adjust the rotating optical element 115 such that thesignal APC_(ref) equals a predetermined value. Alternatively, duringreproduction, APC may be performed by setting the rotating opticalelement 115 and adjusting the output of the light source device 112 suchthat light which has passed through the rotating optical element 115 hasP-polarized components only. When the light-receiving portion of thephotodetector 119 is divided into a plurality of regions and thephase-spatial light modulator 117 is capable of adjusting the quantityof light transmitted thereby, the quantity of light transmitted by eachpixel of the phase-spatial light modulator 117 may be adjusted based ona signal output by each of the light-receiving portions of thephotodetector 119 to adjust the light projected upon the opticalinformation recording medium 1 so as to achieve a uniform intensitydistribution.

The present embodiment may employ: a light source device 112 capable ofemitting laser light in three colors R, G and B; a CCD array 133 capableof detecting light in three colors R, G and B; and an opticalinformation recording medium 1 having three hologram layers whoseoptical characteristics are changed by only light in respective colorsR, G and B. In this case, it is possible to record three kinds ofinformation in the same location of the optical information recordingmedium 1 using the same modulation pattern for the reference light forrecording, which allows multiplex recording of a greater amount ofinformation. For example, recording media having three hologram layersas described above include HRF-700X059-20 (product name) manufactured byDuPont.

When multiplex recording of information is performed using light inthree colors R, G and B as described above, information is recorded ineach of R, G and B colors on a time division basis in the same locationof an optical information recording medium 1. In doing so, while themodulation pattern for the information light is varied for each of R, Gand B colors, the modulation pattern for the reference light forrecording is kept unchanged. When each pixel of information light ineach color carries binary information, i.e., when each pixel is renderedbright or dark, multiplex recording of information using light in threecolors R, G and B makes it possible to record octal (=2³) informationfor each pixel, for example, R being the MSB (most significant bit), Bbeing the LSB (least significant bit). When the spatial light modulator125 is capable of adjusting the quantity of light transmitted thereby inthree or more steps and each pixel of information light in each colorcarries information having n (n is an integer equal to or greater than3) tones, multiplex recording of information using light in three colorsR, G and B makes it possible to record information having n³ values foreach pixel.

Various methods are possible as described below for reproduction ofinformation when the information is recorded on a multiplex basis usinglight in three colors R, G and B. Specifically, if the reference lightfor reproduction is light in any one of R, G and B colors, onlyinformation recorded using light in the same color as the referencelight for reproduction is reproduced. If the reference light forreproduction is light in any two of R, G and B colors, only two kinds ofinformation recorded using light in the same two colors as the referencelight for reproduction are reproduced. The two kinds of information areseparated by the CCD array 133 into information in each color. If thereference light for reproduction is light in three colors R, G and B,three kinds of information recorded using light in the three colors areall reproduced. The three kinds of information are separated by the CCDarray 133 into information in each color. When the optical informationrecording medium 1 has a layer for each of R, G and B colors, multiplexrecording is performed in the layer in each color using phase-encodingmultiplexing. This is advantageous in that it is possible to obtain areproduction image having a pattern in each of the colors R, G and B foreach of phase modulation patterns for the reference light.

A description will now be made with reference to FIGS. 63 and 64 on adirect read after write (hereinafter represented by “DRAW”) function anda write power control (hereinafter represented by “WPC”) function formultiplex recording of the optical information recording/reproducingapparatus according to the present embodiment.

First, the DRAW function will be described. The DRAW function is afunction of reproducing recorded information immediately after theinformation is recorded. This function makes it possible to verifyrecorded information immediately after the information is recorded.

A principle behind the DRAW function according to the present embodimentwill now be described with reference to FIGS. 55 and 57. First, when theDRAW function is used in the present embodiment, a modulation patternfor reference light for recording is used which is in a pointsymmetrical relationship with the center of the phase-spatial lightmodulator 117. During recording, in the hologram layer 225, interferenceoccurs between the A-polarized reference light 311A for recording thathas passed through the optically rotating plate 121L of the doubleoptically rotating plate 121 and the A-polarized information light 312Athat has passed through the optically rotating plate 121R of the doubleoptically rotating plate 121, and interference occurs between theB-polarized reference light 311B for recording that has passed throughthe optically rotating plate 121R of the double optically rotating plate121 and the B-polarized information light 312B that has passed throughthe optically rotating plate 121L of the double optically rotating plate121, resultant interference patterns being volumetrically recorded inthe hologram layer 225.

Thus, when recording of an interference pattern in the hologram layer225 begins, A-polarized reproduction light is generated at the locationwhere the interference pattern is recorded by the reference light 311Bfor recording due to light resulting from the reflection of theA-polarized reference light 311A for recording that has passed throughthe optically rotating plate 121L of the double optically rotating plate121 at the reflecting surface located in the converging position on thefurther side of the hologram layer 225. This reproduction light travelstoward the objective lens 123, passes through the objective lens 123,and thereafter passes through the optically rotating plate 121L of thedouble optically rotating plate 121 to become P-polarized light.Similarly, B-polarized reproduction light is generated at the locationwhere the interference pattern is recorded by the reference light 311Afor recording due to light resulting from the reflection of theB-polarized reference light 311B for recording that has passed throughthe optically rotating plate 121R of the double optically rotating plate121 at the reflecting surface located in the converging position on thefurther side of the hologram layer 225. This reproduction light travelstoward the objective lens 123, passes through the objective lens 123,and thereafter passes through the optically rotating plate 121R of thedouble optically rotating plate 121 to become P-polarized light. Thereproduction light that has passed through the double optically rotatingplate 121 impinges upon the polarization beam splitter 120 and istransmitted by the polarization beam splitter surface 120 a to impingeupon the beam splitter 118. A part of the reproduction light incidentupon the beam splitter 118 is transmitted by the beam splitter surface118 a and passes through the imaging lens 132 to impinge upon the CCDarray 133 at which it is detected. Thus, recorded information can bereproduced immediately after the information is recorded.

The reference number 321 in FIG. 63 represents an example of arelationship between the time that has passed after the start ofrecording of information in one location of an optical informationrecording medium 1 and the output level of the CCD array 133. As can beseen, the output level of the CCD array 133 gradually increases afterthe start of information recording in accordance with the degree of therecording of the interference pattern in the optical informationrecording medium 1, reaches a maximum value at a certain point of timeand gradually decreases thereafter. It can be assumed that recordedinterference pattern (hereinafter referred to as “recorded pattern”) hashigher diffracting efficiency, the higher the output level of the CCDarray 133. It is therefore possible to form a recorded pattern havingdesired diffracting efficiency by stopping recording when the CCD array133 reaches an output level associated with the desired diffractingefficiency.

In the present embodiment, in order to form a recorded pattern havingdesired diffracting efficiency using the DRAW function as describedabove, an appropriate test area is preferably provided in the opticalinformation recording medium 1. A test area is a region whereinformation can be recorded utilizing holography like the data areas 7.Preferably, the controller 90 performs the following operation wheninformation is recorded. Specifically, the controller 90 performs anoperation of recording predetermined test data in the test area inadvance and detects a profile of the output level of the CCD array 133as shown in FIG. 63. At this time, the operations of recording test dataand detecting a profile of the output level of the CCD array 133 arepreferably performed in a plurality of locations in the test area whilechanging the output of the light source device 112 and the ratio betweenreference light for recording and information light. For example, aplurality of profiles are detected as indicated by the reference numbers321 through 323 in FIG. 63; the optimum profile is selected from amongthem; and the actual information recording operation is performed underconditions in accordance with the selected profile.

Based on the detected profile or selected profile, the controller 90identifies the output level associated with desired diffractingefficiency or the time required to reach that output level after thebeginning of the recording. In actual recording of information, thecontroller 90 monitors the output level of the CCD array 133 and stopsthe recording when the output level reaches an output level associatedwith predefined desired diffracting efficiency. Alternatively, in actualrecording of information, the controller 90 stops the recording when atime spent after the start of the recording agrees with the timerequired after the start of recording to reach an output levelassociated with predefined desired diffracting efficiency. Such anoperation makes it possible to form a recorded pattern having desireddiffracting efficiency in an optical information recording medium 1.

As described above, the present embodiment makes it possible to verifyrecorded information using the DRAW function. FIG. 64 shows aconfiguration of a circuit required to perform such verification in anoptical information recording/reproducing apparatus according to thepresent embodiment. As illustrated, the optical informationrecording/reproducing apparatus has: an encoder 331 to which informationto be recorded is supplied by the controller 90 and which encodes theinformation into data for a modulation pattern of the spatial lightmodulator (represented by “SLM” in FIG. 64) 125; a decoder 322 fordecoding data output by the CCD array 133 into data in a format adaptedto be supplied from the controller 90 to the encoder 331; and acomparing portion 333 for comparing the data supplied from thecontroller 90 to the encoder 331 and the data obtained by the decoder322 and for transmitting the information of the result of the comparisonto the controller 90. For example, the comparing portion 333 transmitsinformation of the degree of match between the two items of data to becompared or information of the error rate to the controller 90 as theinformation of the comparison result. For example, the controller 90continues the recording operation if the information of the comparisonresult transmitted by the comparing portion 333 is within a range inwhich data errors can be corrected, and stops the recording operation ifthe information of the comparison result is out of the range in whichdata errors can be corrected.

As described above, since the optical information recording/reproducingapparatus of the present embodiment has the DRAW function, it canperform a recording operation under optimum recording conditions even inthe presence of disturbances such as variation of sensitivity of theoptical information recording medium 1, changes in the ambienttemperature and fluctuation of the output of the light source device112.

Further, the present embodiment allows recording at a high speed withhigh reliability maintained because it has the function of verifyingrecorded information simultaneously with recording of the information.This function is particularly useful in recording information at a hightransfer rate. While the reproduction of unfixed information isunpreferable because it acts similarly to overwrite and can reduce thequality of the recorded information, the verification function of thepresent embodiment creates no problem because verification of recordedinformation is completed during the recording operation.

The WPC function during multiplex recording will now be described. Whena plurality of pieces of information are recorded on a multiplex basisin the same location of an optical information recording medium 1 withthe modulation pattern of the reference light for recording varied, thediffracting efficiency of an early recorded pattern is graduallydecreased by subsequent recording. The WPC function according to thepresent embodiment is a function of controlling reference light forrecording and information light during multiplex recording such thatsubstantially the same diffracting efficiency can be achieved by therecorded pattern of each item of information recorded on a multiplexbasis.

The diffracting efficiency of a recorded pattern depends on parameterssuch as the intensity of the reference light for recording and theinformation light, the illuminating time of the reference light forrecording and the information light, the ratio between the intensity ofthe reference light for recording and the information light, themodulation pattern of the reference light for recording, the totalnumber of times of the recording in the same location of the opticalinformation recording medium 1 and the order of the recording ofinterest. Therefore, the WPC function is required to control at leastone of the plurality of parameters. The control can be simplified bycontrolling the intensity and illuminating time of reference light forrecording and information light. When the intensity of reference lightfor recording and information light is controlled, the intensity isreduced as the recording proceeds. When the illuminating time ofreference light for recording and information light is controlled, theilluminating time is decreased as the recording proceeds.

With the WPC function of the present embodiment, reference light forrecording and information light are controlled at first through m-th (mis an integer equal to or greater than 2) recording operations based ona profile of the output level of the CCD array 133 as shown in FIG. 63which has been obtained in advance. FIG. 63 shows an example ofilluminating times in the case of control over the illuminating time ofreference light for recording and information light. Specifically, inthe example shown in FIG. 63, it is assumed that recording is performedfive times in the same location of an optical information recordingmedium 1, and T₁, T₂, T₃, T₄ and T₅ respectively represents theilluminating time of the reference light for recording and theinformation light at the first, second, third, fourth and fifthrecording.

Thus, the present embodiment makes it possible to provide a recordedpattern of each item of information recorded on a multiplex basis withsubstantially the same diffracting efficiency.

The optical information recording/reproducing apparatus according to thepresent embodiment makes it possible to record a large amount ofinformation in an optical information recording medium 1 with a highdensity. This means that a large amount of information can be lost whena defect or the like occurs in the optical information recording medium1 after information is recorded to disable the reproduction of a part ofthe information. According to the present embodiment, in order toimprove reliability by preventing such loss of information, informationcan be recorded utilizing the RAID (redundant arrays of inexpensivedisks) technique as described below.

The RAID technique is a technique for improving reliability of recordingby recording data with redundancy using a plurality of hard diskdevices. RAIDs are classified into five categories of RAID-1 throughRAID-5. The following description will refer to the RAID-1, RAID-3 andRAID-5 which are typical of the technique, by way of example. RAID-1 isa system in which the same contents are written in two hard disk devicesand which is also referred to as “mirroring”. RAID-3 is a system inwhich input data is divided into parts having a predetermined length tobe recorded in a plurality of hard disk devices and in which parity datais generated and written in another hard disk device. RAID-5 is a systemin which larger units of data division (blocks) are employed; onedivision of data is recorded in one hard disk device as a data block;parity data for data blocks of the hard disk devices associated witheach other is recorded in another hard disk device as a parity block;and the parity block is distributed among all hard disk devices.

A method for recording information utilizing the RAID techniqueaccording to the present embodiment (hereinafter referred to as“distributed recording method”) is to record information in aninterference region 313 of an optical information recording medium 1which is a substitution for a hard disk device in the context of theabove description of RAID.

FIG. 65 is an illustration of an example of the distributed recordingmethod according to the present embodiment. In this example, informationto be recorded in an optical information recording medium 1 is a seriesof data, DATA1, DATA2, DATA3, . . . , and the same data DATA1, DATA2,DATA3, . . . are recorded in a plurality of interference regions 313 athrough 313 e of the optical information recording medium 1. A pluralityof items of data are recorded on a multiplex basis in each of theinterference regions 313 a through 313 e using phase-encodingmultiplexing. This method of recording corresponds to RAID-1. Accordingto this method of recording, even if reproduction of data is disabled inany of the plurality of interference regions 313 a through 313 e, thedata can be reproduced from other interference regions.

FIG. 66 is an illustration of another example of the distributedrecording method according to the present embodiment. In this example,information to be recorded in an optical information recording medium 1is a series of data, DATA1, DATA2, DATA3, . . . , DATA12; the data aredivided and recorded in a plurality of interference regions 313 athrough 313 d; parity data for the data recorded in the plurality ofinterference regions 313 a through 313 d are generated; and the paritydata are recorded in an interference region 313 e. More specifically,according to this method of recording, the data DATA1 through DATA4 arerecorded in the interference regions 313 a through 313 d respectively;parity data PARITY(1–4) for the data DATA1 through DATA4 are recorded inthe interference region 313 e; the data DATA5 through DATA8 are recordedin the interference regions 313 a through 313 d respectively; paritydata PARITY(5–8) for the data DATA5 through DATA8 are recorded in theinterference region 313 e; the data DATA9 through DATA12 are recorded inthe interference regions 313 a through 313 d respectively; and paritydata PARITY(9–12) for the data DATA9 through DATA12 are recorded in theinterference region 313 e. A plurality of items of data are recorded ona multiplex basis in each of the interference regions 313 a through 313e using phase-encoding multiplexing. This method of recordingcorresponds to RAID-3. According to this method of recording, even ifreproduction of data is disabled in any of the plurality of interferenceregions 313 a through 313 e, the data can be restored using the paritydata recorded in the interference region 313 e.

FIG. 67 is an illustration of another example of the distributedrecording method according to the present embodiment. In this example,information to be recorded in an optical information recording medium 1is a series of data, DATA1, DATA2, DATA3, . . . , DATA12; the data aredivided and recorded in four interference regions among a plurality ofinterference regions 313 a through 313 e; parity data for the recordeddata are generated; and the parity data are recorded in the remaininginterference region among the plurality of interference regions 313 athrough 313 e. According to this method of recording, the interferenceregion to record the parity data is sequentially changed. Morespecifically, according to this method of recording, the data DATA1through DATA4 are recorded in the interference regions 313 a through 313d respectively; parity data PARITY(1–4) for the data DATA1 through DATA4are recorded in the interference region 313 e; the data DATA5 throughDATA8 are recorded in the interference regions 313 a through 313 c and313 e respectively; parity data PARITY(5–8) for the data DATA5 throughDATA8 are recorded in the interference region 313 d; the data DATA9through DATA12 are recorded in the interference regions 313 a, 313 b,313 d and 313 e respectively; and parity data PARITY(9–12) for the dataDATA9 through DATA12 are recorded in the interference region 313 c. Aplurality of items of data are recorded on a multiplex basis in each ofthe interference regions 313 a through 313 e using phase-encodingmultiplexing. This method of recording corresponds to RAID-5. Accordingto this method of recording, even if reproduction of data is disabled inany of the plurality of interference regions where data are recorded,the data can be restored using the parity data.

For example, the distributed recording methods as shown in FIGS. 65through 67 are carried out under the control of the controller 90 ascontrol means.

FIG. 68 shows an example of an arrangement of a plurality ofinterference regions used in the distributed recording method asdescribed above. In this example, interference regions used for thedistributed recording method are a plurality of interference regions 313adjacent to each other in one track. In this case, the plurality ofinterference regions 313 used for the distributed recording method arepreferably interference regions within a range for which in-field accessis possible. The reason is that it allows high speed access to each ofthe interference regions 313.

FIG. 69 shows another example of an arrangement of a plurality ofinterference regions used in the distributed recording method asdescribed above. In this example, interference regions used for thedistributed recording method are a plurality of interference regions 313which are two-dimensionally adjacent to each other in the radialdirection 331 of the optical information recording medium 1 and in thedirection 332 of the tracks thereof. In this case, among the pluralityof interference regions used for the distributed recording method, aplurality of interference regions 313 adjacent to each other in thedirection 332 of the tracks are preferably interference regions within arange for which in-field access is possible. The reason is that itallows high speed access to each of the interference regions 313 whichare adjacent to each other in the direction 332 of the tracks.

According to the distributed recording methods in the presentembodiment, a series of data may be recorded in a distributed manner ina plurality of discrete interference regions 313 instead of recordingthem in a plurality of interference regions 313 adjacent to each other.

While a description has been made so far on distributed recordingmethods for recording a plurality of items of data in a singleinterference region 313 on a multiplex basis utilizing phase-encodingmultiplexing, a distributed recording method can be implemented alsowhen a plurality of items of data are recorded on a multiplex basisusing other methods. By way of example, a description will be made withreference to FIG. 70 on a distributed recording method for multiplexrecording of a plurality of items of data using a method referred to as“shift multiplexing”. As shown in FIG. 70, shift multiplexing is amethod for recording a plurality of pieces of information on a multiplexbasis by forming a plurality of interference regions 313 in an opticalinformation recording medium 1 such that they are slightly shifted fromeach other and are partially overlapped with each other in thehorizontal direction. While FIG. 70 shows an example in which aplurality of interference regions 313 used for the distributed recordingmethod are two-dimensionally arranged, the plurality of interferenceregions 313 used for the distributed recording method may be arrangedsuch that they are adjacent to each other in the same track. In FIG. 70,the arrow indicated by the reference number 334 represents an order ofrecording. According to the distributed recording method utilizingmultiplexing, data and parity data divided from a series of data arerecorded in a plurality of interference regions 313 in a distributedmanner.

A distributed recording method can be implemented also when a pluralityof items of data are recorded on a multiplex basis using phase-encodingmultiplexing and shift multiplexing in combination. FIG. 71 shows anexample in which interference regions 313 for multiplex recording ofinformation utilizing phase-encoding multiplexing are formed with nooverlap between them in the direction 332 of the tracks of an opticalinformation recording medium 1 and in which adjoining interferenceregions 313 to be used for shift multiplexing are formed in the radialdirection 331 of the optical information recording medium 1 such thatthey are slightly shifted from each other and are partially overlappedwith each other in the horizontal direction. Each of the interferenceregions 313 in this example is treated similarly to the interferenceregions 313 a through 313 e in FIGS. 65 through 67.

A description will now be made with reference to FIGS. 72 and 73 on ajuke apparatus utilizing an optical information recording/reproducingapparatus according to the present embodiment as an example of theapplication of an optical information recording/reproducing apparatusaccording to the present embodiment. A juke apparatus is an informationrecording/reproducing apparatus of a large capacity having anauto-changer mechanism for changing recording media.

FIG. 72 is a perspective view showing the exterior of the jukeapparatus, and FIG. 73 is a block diagram of a circuit configuration ofthe juke apparatus. The juke apparatus has: a front panel block 401provided on the front side of the juke apparatus; a robotics block 402that forms the interior of the juke apparatus; a rear panel block 403provided on the rear side of the juke apparatus; a first disk array 404provided inside the juke apparatus and constituted by a plurality ofoptical information recording/reproducing apparatuses coupled to eachother; a second disk array 405 similarly constituted by a plurality ofoptical information recording/reproducing apparatuses coupled to eachother; and a power supply block 406 for supplying predetermined power toeach part of the juke apparatus.

The front panel block 401 has a front door 407 which is opened andclosed for purposes such as changing disk arrays 404 and 405, and afront panel 408.

On the front panel 408, there is provided a keypad 409 having variousoperating keys; a display 410 for displaying modes of operation and thelike; a functional switch 411 for instructing opening and closing of thefront door 407; a mail slot 412 which is a port to insert and eject anoptical information recording medium 1; a transfer motor 413 fortransferring an optical information recording medium 1 inserted throughthe mail slot 412 to a mail box which is not shown and for transferringan optical information recording medium 1 to be ejected from the mainbox to the mail slot 412; and a full sensor 414 for detecting that thenumber of optical information recording media 1 inserted into the jukeapparatus has reached a predefined number.

On the front door 407, there is provided a door sensor 415 for detectingopened and closed states of the front door 407; a door lock solenoid 416for controlling the opening and closing of the front door 407; and aninterlock switch 417 for controlling the opening and closing of thefront door 407 in accordance with operations on the functional switch411.

The robotics block 402 has: a lower magazine 421 capable of containing,for example, ten optical information recording media 1; an uppermagazine 422 stacked on top of the lower magazine 421 and capable ofcontaining, for example, ten optical information recording media 1; anda controller block 423 for controlling the juke apparatus as a whole.

The robotics block 402 further has: a grip operation motor 424 forcontrolling a grip operation of a manipulator which is not shown to movean optical information recording medium 1 inserted into the jukeapparatus to a predetermined location; a grip operation motor controller425 for controlling the rotating speed and direction of the gripoperation motor 424 under the control of the controller block 423; and agrip operation encoder 426 for detecting the rotating speed anddirection of the grip operation motor 424 and for supplying the detecteddata to the controller block 423. Further, the robotics block 402 has: arotating operation motor 427 for controlling the manipulator forrotation in a clockwise direction, a counterclockwise direction or inboth directions; a rotating operation motor controller 428 forcontrolling the rotating speed and direction of the rotating operationmotor 427 under the control of the controller block 423; and a rotatingoperation encoder 429 for detecting the rotating speed and direction ofthe rotating operation motor 427 and for supplying the detected data tothe controller block 423. The robotics block 402 further has: a verticaloperation motor 430 for controlling upward and downward movements of themanipulator; a vertical operation motor controller 431 for controllingthe rotating speed and direction of the vertical operation motor 430under the control of the controller block 423; and a vertical operationencoder 432 for detecting the rotating speed and direction of thevertical operation motor 430 and for supplying the detected data to thecontroller block 423.

The robotics block 402 further has: a transfer motor controller 433 forcontrolling the rotating speed and direction of the transfer motor 413for the operation of inserting and ejecting optical informationrecording media 1 through the mail slot 412; a clear pass sensor 434;and a clear pass emitter 420.

The rear panel block 403 has: an RS232C connector terminal 435 which isan input/output terminal for serial transmission; a UPS (uninterruptiblepower system) connector terminal 436; a first SCSI (small computersystem interface) connector terminal 437 which is an input/outputterminal for parallel transmission; a second SCSI connector terminal 438which is also an input/output terminal for parallel transmission; and anAC (alternating current) power supply connector terminal 439 connectedto a mains power supply.

Each of the RS232C connector terminal 435 and UPS connector terminal 436is connected to the controller block 423. The controller block 423converts serial data supplied through the RS232C connector terminal 435into parallel data and supplies the data to the disk arrays 404 and 405.It also converts parallel data from disk arrays 404 and 405 into serialdata and supplies the data to the RS232C connector terminal 435.

Each of the SCSI connector terminals 437 and 438 is connected to thecontroller block 423 and disk arrays 404 and 405. The disk arrays 404and 405 exchange data directly through the SCSI connector terminals 437and 438, and the controller block 423 converts parallel data from thedisk arrays 404 and 405 into serial data and supplies the data to theRS232C connector terminal 435.

The AC power supply connector terminal 439 is connected to the powersupply block 406. The power supply block 406 generates power of +5 V,+12 V, +24 V and −24 V based on the mains power supply obtained throughthe AC power supply connector terminal 439 and supplies the power toother blocks.

The manipulator which is not shown has a carriage having a gripper forperforming operations such as picking up optical information recordingmedia 1 transferred to the mail box through the mail slot 412 one byone, a carriage holding portion for holding the carriage, and a drivingportion for controlling the carriage for vertical, horizontal,back-and-forth and rotary movements. Inside the juke apparatus, there isprovided four columns which define a substantially rectangularconfiguration on the bottom thereof and which are erected to extendperpendicularly to the bottom from the four corners of the rectangularconfiguration to the top surface of the juke apparatus. The carriageholding portion holds the carriage such that it can make lateral, backand forth and rotary movements and has column gripping portions on bothends thereof for gripping the columns to allow the carriage holdingportion to move vertically along the four columns.

The carriage driving portion generates a driving force to control such amanipulator for vertical movements along the columns, generates adriving force to control the carriage for lateral, back and forth androtary movements and generates a driving force to pick up an opticalinformation recording medium 1 with the gripper.

As shown in FIG. 72, the front door 407 is cantilevered by a hinge 450at one end thereof to be able to open and close, and each of the lowermagazine 421, the upper magazine 422 and the first and second diskarrays 404 and 405 can be pulled out or loaded by opening and closingthe front door 407. Each of the magazines 421 and 422 has a boxyconfiguration for containing ten optical information recording media 1each housed in a cartridge in the form of a stack in parallel with thebottom of the juke apparatus, and an optical information recordingmedium 1 is inserted from the rear side of each of the magazines 421 and422 (the side of each of the magazines 421 and 422 that is opposite tothe front side thereof where the front door 407 is located when it ismounted in the juke apparatus). Optical information recording media 1can be mounted at one time by a user removing the magazines 421 and 422to load it manually and mounting the magazines 421 and 422 loaded withthe optical information recording media 1 in the juke apparatus. Whenoptical information recording media 1 are inserted through the mail slot412, the inserted optical information recording media 1 are transferredto the mail box, and the optical information recording media 1transferred to the mail box are loaded by the manipulator into themagazines 421 and 422. Thus, optical information recording media 1 canbe automatically loaded into the magazines 421 and 422.

Each of the first and second disk arrays 404 and 405 has a RAIDcontroller and a drive array formed by coupling first through fifthoptical information recording/reproducing apparatuses.

Each of the optical information recording/reproducing apparatuses has adisk insertion/ejection port, and optical information recording media 1are inserted in and ejected from each of the optical informationrecording/reproducing apparatuses through the disk insertion/ejectionport. The RAID controllers are connected to the controller block 423 andcontrol the optical information recording/reproducing apparatusesaccording to the recording method of RAID-1, RAID-3 or RAID-5 under thecontrol of the controller block 423. Each of the recording methods ofRAID-1, RAID-3 and RAID-5 is selected through a key operation on thekeypad 409 provided on the front panel 408.

In this juke apparatus, data are recorded using the disk arrays 404 and405 in accordance with the recording method of RAID-1, RAID-3 or RAID-5.In order to record data in such a manner, optical information recordingmedia 1 must be loaded in the juke apparatus in advance. There are twomethods for loading the juke apparatus with the optical informationrecording media 1.

As shown in FIG. 72, a first method of loading is a method wherein thefront door 407 is opened to remove the lower magazine 421 and the uppermagazine 422 and optical information recording media 1 are manuallyloaded in the magazines 421 and 422.

A second method of loading is a method wherein optical informationrecording media 1 are loaded one by one through the mail slot 412 asshown in FIG. 73. When an optical information recording medium 1 isloaded into the mail slot 412, the controller block 423 detects it andcontrols the driving of the transfer motor 413 to transfer the opticalinformation recording medium 1 to the mail box. When the opticalinformation recording medium 1 is transferred to the mail box, thecontroller block 423 controls the driving of the vertical operationmotor 430 to move the manipulator toward the mail box and controls thedriving of the grip operation motor 424 to move the optical informationrecording medium 1 picked up by the gripper provided on the manipulatorto a vacant disk housing portion of the magazine 421 or 422. The drivingof the grip operation motor 424 is controlled to release the opticalinformation recording medium 1 held by the gripper in the disk housingportion. The controller block 423 controls each portion to repeat such aseries of operations each time an optical information recording medium 1is inserted through the mail slot 412.

When the magazines 421 and 422 are thus loaded with optical informationrecording media 1 according to the first or second method of loading,the controller block 423 controls the manipulator to transfer theoptical information recording media 1 contained in the lower magazine421 or the upper magazine 422 to the first disk array 404 or the seconddisk array 405. Each of the disk arrays 404 and 405 can be loaded withfive optical information recording media 1 and, therefore, five out ofthe total of twenty optical information recording media 1 contained inthe magazines 421 and 422 are loaded in the first disk array 404, andanother five are loaded in the second disk array 405 by the manipulator.

To record data, a user operates the keypad 409 to select a desiredrecording method from among the RAID-1, RAID-3 and RAID-5 recordingmethods and operates the keypad 409 to instruct the start of datarecording. The data to be recorded are supplied to the disk arrays 404and 405 through the RS232C connector terminal 435 or the first andsecond SCSI connector terminals 437 and 438. When the start of datarecording is instructed, the controller block 423 controls the diskarrays 404 and 405 through the RAID controllers provided at the diskarrays 404 and 405 to enable recording of data according to the selectedrecording method.

In this juke apparatus, five optical information recording/reproducingapparatuses provided for each of the disk arrays 404 and 405 aresubstituted for hard disk devices in a conventional RAID utilizing harddisk devices to record data according to a recording method selectedfrom among the RAID-1, RAID-3 and RAID-5 recording methods. The datainterfaces of this juke apparatus are not limited to those mentioned inthe above description.

The optical information recording/reproducing apparatus according to thepresent embodiment makes it possible to achieve copy protection andsecurity easily like the first embodiment.

It is also possible to provide information distribution services e.g., aservice in which optical information recording media 1 having amultiplicity of kinds of information (e.g., various kinds of software)recorded thereon with different modulation patterns for reference lightare provided to users and in which pieces of information of thereference light modulation patterns to enable reproduction of each ofthe various kinds of information are separately sold to the users as keyinformation as requested by the users.

Phase modulation patterns for reference light to serve as the keyinformation to retrieve predetermined information from an opticalinformation recording medium I may be created based on informationspecific to a person who is a user. Such information specific to aperson includes a secret number, a fingerprint, a voiceprint and an irispattern.

FIG. 74 shows an example of a configuration of major parts of an opticalinformation recording/reproducing apparatus according to the presentembodiment in which phase modulation patterns for reference light arecreated based on personal information as described above. In thisexample, the optical information recording/reproducing apparatus has: apersonal information input portion 501 for inputting informationspecific to a person such as a fingerprint; a phase modulation patternencoder 502 for creating a phase modulation pattern for reference lightbased on the information input through the personal information inputportion 501 and for supplying information on the created modulationpattern to the phase-spatial light modulator 117 as desired wheninformation is recorded or reproduced to drive the phase-spatial lightmodulator 117; and a card issuing and input portion 503 for issuing acard 504 on which the information on the modulation pattern created bythe phase modulation pattern encoder 502 is recorded and for sending theinformation on the modulation pattern recorded on the card 504 to thephase modulation pattern encoder 502 when the card 504 is loadedtherein.

In the example shown in FIG. 74, when a user inputs information specificto the person such as a fingerprint to the personal information inputportion 501 to record information in an optical information recordingmedium 1 using the optical information recording/reproducing apparatusaccording to the present embodiment, the phase modulation patternencoder 502 creates a phase modulation pattern for reference light basedon the information input through the personal information input portion501 and supplies information on the created modulation pattern to thephase-spatial light modulator 117 to drive the phase-spatial lightmodulator 117 during the recording of the information. As a result, theinformation is recorded in the optical information recording medium 1 inassociation with the phase modulation pattern for reference lightcreated based on the information specific to the person who is the user.The phase modulation pattern encoder 502 transmits the information onthe created modulation pattern to the card issuing and input portion503, and the card issuing and input portion 503 issues a card 504 onwhich the transmitted information on the modulation pattern is recorded.

To reproduce the information recorded as described above from theoptical information recording medium 1, the user either inputs theinformation specific to the person to the personal information inputportion 501 as in recording, or loads the card 504 into the card issuingand input portion 503.

When the information specific to the person is input to the personalinformation input portion 501, the phase modulation pattern encoder 502creates a phase modulation pattern for reference light based on theinformation input through the personal information input portion 501 andsupplies information on the created modulation pattern to thephase-spatial light modulator 117 to drive the phase-spatial lightmodulator 117 during the reproduction of the information. At this time,if the phase modulation pattern for the light at recording agrees withthe phase modulation pattern for reference light at reproduction, thedesired information is reproduced. In order to prevent the phasemodulation pattern encoder 502 from creating different modulationpatterns at recording and reproduction in spite of the fact that thesame information specific to the person is input to the personalinformation input portion 501, the phase modulation pattern encoder 502may be adapted to create the same modulation pattern even if there issome difference between the pieces of information input through thepersonal information input portion 501.

When the card 504 is loaded into the card issuing and input portion 503,the card issuing and input portion 503 transmits the information on themodulation pattern recorded on the card 504 to the phase modulationpattern encoder 502, and the phase modulation pattern encoder 502supplies the transmitted information on the modulation pattern to thephase-spatial light modulator 117 to drive the phase-spatial lightmodulator 117. Thus, the desired information is reproduced.

The configuration, operation and effects of the present embodiment areotherwise substantially the same as those of the first embodiment.

The present invention is not limited to the above-described embodimentsand may be modified in various ways. For example, address informationand the like is recorded in advance in the address servo areas 6 of theoptical information recording medium 1 in the form of embossed pits inthe above-described embodiments; however, instead of providing embossedpits in advance, formatting may alternatively be carried out byselectively illuminating regions near the protective layer 4 of thehologram layer 3 in the address servo areas 6 with high power laserlight to selectively change the refractivity of such regions, therebyrecording address information and the like.

As the element for detecting information recorded in the hologram layer3, a smart optical sensor in which a MOS type solid state image pick-upelement and a signal processing circuit are integrated on a single chip(see an article “O plus E, September, 1996, No. 202”, pp. 93–99 by wayof example) may be used instead of a CCD array. Since such a smartoptical sensor has a high transfer rate and a high speed operatingfunction, the use of such a smart optical sensor allows high speedreproduction, e.g., reproduction at a transfer rate on the order ofGbit/sec.

Especially, when a smart optical sensor is used as the element fordetecting information recorded in the hologram layer 3, instead ofrecording address information and the like in the address servo areas 6of the optical information recording medium 1 using embossed pits inadvance, address information and the like in a predetermined pattern maybe recorded in advance using the same method as for recording in thedata areas 7 utilizing holography, in which case the address informationand the like is detected by the smart optical sensor during a servooperation with the pick-up set in the same state as in reproduction. Inthis case, a basic clock and address can be directly obtained from thedata detected by the smart optical sensor. A tracking error signal canbe obtained from information of the position of a reproduction patternon the smart optical sensor. Focus servo can be performed by driving theobjective lens 12 so as to maximize the contrast of the reproductionpattern on the smart optical sensor. Focus servo can be performed alsoduring reproduction by driving the objective lens so as to maximize thecontrast of a reproduction pattern on the smart optical sensor.

In the above-described embodiments, information on the modulationpattern of reference light and information on the wavelength thereof maybe supplied to the controller 90 from an external host apparatus.

As described above, in the first optical information recording apparatusor optical information recording method according to the invention, theinformation recording layer is illuminated with information lightcarrying information and reference light for recording having aspatially modulated phase on the same side thereof, which isadvantageous in that information can be recorded on a multiplex basisutilizing phase-encoding multiplexing and in that the optical system forrecording can be configured compactly.

The first optical information recording apparatus according to theinvention is further advantageous in that light for recording can bepositioned with high accuracy by controlling the positions ofinformation light and reference light for recording relative to theoptical information recording medium using information recorded in apositioning region of the optical information recording medium.

In the first optical information recording apparatus according to theinvention, the recording optical system projects information light andreference light for recording such that the optical axis of theinformation light and the optical axis of the reference light forrecording are located on the same line, which provides another advantagein that the optical system for recording can be configured morecompactly.

In the first optical information recording apparatus according to theinvention, the information light generation means generates informationlight in a plurality of wavelength bands, and the recording referencelight generation means generates reference light for recording in thesame plurality of wavelength bands as those for the information light,which provides another advantage in that more information can berecorded on a multiplex basis.

The first optical information recording apparatus according to theinvention has control means for controlling the information lightgeneration means and the recording reference light generation means suchthat information is recorded with redundancy in the optical informationrecording medium, which provides another advantage in that reliabilitycan be improved.

In the first optical information reproducing apparatus or opticalinformation reproducing method according to the invention, theinformation recording layer is illuminated with reference light forreproduction having a spatially modulated phase; reproduction lightgenerated at the information recording layer when illuminated with thereference light for reproduction is collected on the same side of theinformation recording layer that is illuminated with the reference lightfor reproduction; and the collected reproduction light is detected. Thisis advantageous in that information recorded on a multiplex basisutilizing phase-encoding multiplexing can be reproduced and in that theoptical system for reproduction can be configured compactly.

The first optical information reproducing apparatus according to theinvention is further advantageous in that light for reproduction can bepositioned with high accuracy by controlling the position of thereference light for reproduction relative to the optical informationrecording medium using information recorded in a positioning region ofthe optical information recording medium.

In the first optical information reproducing apparatus according to theinvention, the reproducing optical system projects reference light forreproduction and collects reproduction light such that the optical axisof the reference light for reproduction and the optical axis of thereproduction light are located on the same line, which provides anotheradvantage in that the optical system for reproduction can be configuredmore compactly.

In the first optical information reproducing apparatus according to theinvention, the reproduction reference light generation means generatesreference light for reproduction in a plurality of wavelength bands, andthe detection means detects reproduction light in the same plurality ofwavelength bands as those for the reference light for reproduction,which provides another advantage in that it is possible to reproduceinformation recorded using reference light for recording and informationlight in a plurality of wavelength bands.

In the second optical information recording apparatus or opticalinformation recording method according to the invention, the informationrecording layer is illuminated with information light having a selectedwavelength and carrying information and reference light for recordinghaving a selected wavelength on the same side thereof, which isadvantageous in that information can be recorded on a multiplex basisutilizing wavelength multiplexing and in that the optical system forrecording can be configured compactly.

The second optical information recording apparatus according to theinvention is further advantageous in that light for recording can bepositioned with high accuracy by controlling the positions ofinformation light and reference light for recording relative to theoptical information recording medium using information recorded in apositioning region of the optical information recording medium.

In the second optical information recording apparatus according to theinvention, the recording optical system projects information light andreference light for recording such that the optical axis of theinformation light and the optical axis of the reference light forrecording are located on the same line, which provides another advantagein that the optical system for recording can be configured morecompactly.

In the second optical information reproducing apparatus or opticalinformation reproducing method according to the invention, theinformation recording layer is illuminated with reference light forreproduction having a selected wavelength; reproduction light generatedat the information recording layer when illuminated with the referencelight for reproduction is collected on the same side of the informationrecording layer that is illuminated with the reference light forreproduction; and the collected reproduction light is detected. This isadvantageous in that information recorded on a multiplex basis utilizingwavelength multiplexing can be reproduced and in that the optical systemfor reproduction can be configured compactly.

The second optical information reproducing apparatus according to theinvention is further advantageous in that light for reproduction can bepositioned with high accuracy by controlling the position of referencelight for reproduction relative to the optical information recordingmedium using information recorded in a positioning region of the opticalinformation recording medium.

In the second optical information reproducing apparatus according to theinvention, the reproducing optical system projects reference light forreproduction and collects reproduction light such that the optical axisof the reference light for reproduction and the optical axis of thereproduction light are located on the same line, which provides anotheradvantage in that the optical system for reproduction can be configuredmore compactly.

In the third optical information recording apparatus or opticalinformation recording method according to the invention, the informationrecording layer is illuminated with information light having a selectedwavelength and carrying information and reference light for recordinghaving a selected wavelength and having a spatially modulated phase onthe same side thereof, which is advantageous in that information can berecorded on a multiplex basis utilizing wavelength multiplexing andphase-encoding multiplexing and in that the optical system for recordingcan be configured compactly.

The third optical information recording apparatus according to theinvention is further advantageous in that light for recording can bepositioned with high accuracy by controlling the positions ofinformation light and reference light for recording relative to theoptical information recording medium using information recorded in apositioning region of the optical information recording medium.

In the third optical information recording apparatus according to theinvention, the recording optical system projects information light andreference light for recording such that the optical axis of theinformation light and the optical axis of the reference light forrecording are located on the same line, which provides another advantagein that the optical system for recording can be configured morecompactly.

In the third optical information reproducing apparatus or opticalinformation reproducing method according to the invention, theinformation recording layer is illuminated with reference light forreproduction having a selected wavelength and having a spatiallymodulated phase; reproduction light generated at the informationrecording layer when illuminated with the reference light forreproduction is collected on the same side of the information recordinglayer that is illuminated with the reference light for reproduction; andthe collected reproduction light is detected. This is advantageous inthat information recorded on a multiplex basis utilizing wavelengthmultiplexing and phase-encoding multiplexing can be reproduced and inthat the optical system for reproduction can be configured compactly.

The third optical information reproducing apparatus according to theinvention is further advantageous in that light for reproduction can bepositioned with high accuracy by controlling the position of referencelight for reproduction relative to the optical information recordingmedium using information recorded in a positioning region of the opticalinformation recording medium.

In the third optical information reproducing apparatus according to theinvention, the reproducing optical system projects reference light forreproduction and collects reproduction light such that the optical axisof the reference light for reproduction and the optical axis of thereproduction light are located on the same line, which provides anotheradvantage in that the optical system for reproduction can be configuredmore compactly.

In the fourth optical information recording apparatus according to theinvention, the pick-up device provided in a face-to-face relationshipwith the optical information recording medium projects information lightand reference light for recording upon the information recording layeron the same side thereof to record information in the informationrecording layer using an interference pattern as a result ofinterference between the information light and the reference light forrecording, which is advantageous in that the optical system forrecording can be configured compactly and in that random access to theoptical information recording medium can be performed easily.

In the fourth optical information recording apparatus according to theinvention, the recording optical system projects information light andreference light for recording such that the optical axis of theinformation light and the optical axis of the reference light forrecording are located on the same line, which provides another advantagein that the optical system for recording can be configured morecompactly.

In the fourth optical information recording apparatus according to theinvention, the light source emits beams of light in a plurality ofwavelength bands, which provides another advantage in that moreinformation can be recorded on a multiplex basis.

In the fourth optical information recording apparatus according to theinvention, the pick-up device has first light quantity monitoring meansfor monitoring the quantity of information light and second lightquantity monitoring means for monitoring the quantity of reference lightfor recording, which provides another advantage in that the quantitiesof the information light and the reference light for reproduction can beindependently monitored and controlled.

In the fourth optical information recording apparatus according to theinvention, the pick-up device has reproduction light detection means fordetecting reproduction light as a result of diffraction of referencelight for recording caused by an interference pattern formed in theinformation recording layer during the recording of information in theinformation recording layer, which provides another advantage in thatrecorded information can be verified immediately after the recording ofthe information.

The fourth optical information recording apparatus according to theinvention has control means for controlling the recording operationbased on information on reproduction light detected by reproductionlight detection means, which provides another advantage in that therecording operation can be performed in an optimum recording state.

The fourth optical information recording apparatus according to theinvention has control means for controlling illuminating conditions forinformation light and reference light for recording during multiplexrecording based on information on reproduction light detected byreproduction light detection means, which provides another advantage inthat multiplex recording can be performed under optimum conditions.

In the fourth optical information recording apparatus according to theinvention, the pick-up device has fixing means for fixing informationrecorded using an interference pattern in the information recordinglayer, which provides another advantage in that information can befixed.

In the fourth optical information recording apparatus according to theinvention, an optical information recording medium is used which has arecording region that allows recording of information using aninterference pattern and positioning regions provided on both sides ofthe recording region for positioning information light and referencelight for recording, and control means is provided for reciprocating theilluminating positions of the information light and the reference lightfor recording by way of the recording region and at least a part of thepositioning regions on both sides thereof to position the informationlight and the reference light for recording relative to the recordingregion based on information obtained from the positioning regions. Thisprovides another advantage in that it is possible to prevent shift of arecording position even when recording is performed for a relativelylong time in the same location of an optical information recordingmedium.

In the fourth optical information recording apparatus according to theinvention, by providing a plurality of pick-up devices, anotheradvantage is achieved in that simultaneous recording can be performed ona single optical information recording medium with the plurality ofpick-up devices to improve recording performance.

In the fourth optical information reproducing apparatus according to theinvention, the pick-up device provided in a face-to-face relationshipwith an optical information recording medium projects reference lightfor reproduction upon the information recording layer; reproductionlight generated at the information recording layer when illuminated withthe reference light for reproduction is collected on the same side ofthe information recording layer that is illuminated with the referencelight for reproduction; and the reproduction light is detected, which isadvantageous in that the optical system for reproduction can beconfigured compactly and in that random access to the opticalinformation recording medium can be performed easily.

In the fourth optical information reproducing apparatus according to theinvention, the reproducing optical system projects the reference lightfor reproduction and collects reproduction light such that the opticalaxis of the reference light for reproduction and the optical axis of thereproduction light are located on the same line, which provides anotheradvantage in that the optical system for reproduction can be configuredmore compactly.

In the fourth optical information reproducing apparatus according to theinvention, the light source emits beams of light in a plurality ofwavelength bands, and detection means detects reproduction light in thesame plurality of wavelength bands as those for the beams of lightemitted by the light source. This provides another advantage in that itis possible to reproduce information recorded in an optical informationrecording medium on a multiplex basis using light in a plurality ofwavelength bands.

In the fourth optical information reproducing apparatus according to theinvention, the pick-up device has light quantity monitoring means formonitoring the quantity of reference light for reproduction, whichprovides another advantage in that the quantity of the reference lightfor reproduction can be monitored and controlled.

In the fourth optical information reproducing apparatus according to theinvention, an optical information recording medium is used which has arecording region that allows recording of information using aninterference pattern and positioning regions provided on both sides ofthe recording region for positioning reference light for reproduction,and control means is provided for reciprocating the illuminatingposition of the reference light for reproduction by way of the recordingregion and at least a part of the positioning regions on both sidesthereof to position the reference light for reproduction relative to therecording region based on information obtained from the positioningregions. This provides another advantage in that it is possible toprevent shift of a reproducing position even when reproduction isperformed for a relatively long time in the same location of an opticalinformation recording medium.

In the fourth optical information reproducing apparatus according to theinvention, by providing a plurality of pick-up devices, anotheradvantage is achieved in that simultaneous reproduction can be performedon a single optical information recording medium with the plurality ofpick-up devices to improve reproducing performance.

In the optical information recording/reproducing apparatus according tothe invention, during recording, the pick-up device provided in aface-to-face relationship with the optical information recording mediumprojects information light and reference light for recording upon theinformation recording layer on the same side thereof to recordinformation in the information recording layer using an interferencepattern as a result of interference between the information light andthe reference light for recording. During reproduction, the pick-updevice illuminates the information recording layer with reference lightfor reproduction; reproduction light generated at the informationrecording layer when illuminated with the reference light forreproduction is collected on the same side of the information recordinglayer that is illuminated with the reference light for reproduction; andthe collected reproduction light is detected. This is advantageous inthat the optical system for recording and reproduction can be configuredcompactly and in that random access to the optical information recordingmedium can be performed easily.

In the optical information recording/reproducing apparatus according tothe invention, by providing a plurality of pick-up devices, anotheradvantage is achieved in that simultaneous recording and reproductioncan be performed on a single optical information recording medium withthe plurality of pick-up devices to improve recording and reproducingperformance.

The optical information recording medium according to the invention has:a first information layer for recording information in the form of aninterference pattern as a result of interference between informationlight and reference light for recording utilizing holography and forgenerating reproduction light associated with the recorded informationwhen illuminated with reference light for reproduction; and a secondinformation layer which is provided in a position different from theposition of the first information layer in the direction of thethickness and in which information is recorded using means differentfrom that for the recording of information in the first informationlayer. This is advantageous in that the positioning of informationlight, reference light for recording and reference light forreproduction relative to the first information layer can be performedusing the information recorded in the second information layer, and inthat directory information, directory management information and thelike on the information recorded in the first information layer can berecorded in the second information layer to make it possible to performrandom access and high density recording easily.

In the optical information recording medium according to the invention,a gap having a predetermined thickness is formed between the firstinformation layer and the second information layer, which providesanother advantage in that a sufficiently large interference region canbe formed between reference light for recording and information light inthe first information layer while allowing reproduction of informationrecorded in the second layer.

It will be understood from the above description that the invention maybe carried out in various modes and modified modes. Therefore, thepresent invention may be carried out in modes other than theabove-described best modes for carrying out the invention within thescope of equivalence of the appended claims.

1. An optical information recording apparatus for recording informationin an optical information recording medium having reflecting layer andinformation recording layer in which information is recorded utilizingholography, the apparatus comprising: a pick-up device provided in aface-to-face relationship with the optical information recording medium,the pick-up device comprising: a light source; an information lightgeneration means for generating information light carrying twodimensional digital pattern information using the beams of light emittedby the light source; a recording reference light generation meansincluding modulation means for spatially modulating the beams of lightemitted by the light source, for generating reference light forrecording being spatially modulated by the modulation means; and arecording optical system including only one objective lens forprojecting the information light generated by the information lightgeneration means and the reference light for recording generated by therecording reference light generation means upon the optical informationrecording medium, for illuminating the information recording layer onthe same side thereof with the information light and the reference lightfor recording such that the information is recorded in the informationrecording layer in the form of an interference pattern as a result ofusing the reflecting layer as a reference plane to generate interferencebetween the information light and the reference light for recording,wherein the recording optical system projects the information light andthe reference light for recording such that an optical axis of theinformation light and an optical axis of the reference light forrecording are located on a same line.
 2. An optical informationrecording apparatus according to claim 1, wherein the modulation meansof the recording reference light generation means modulates the phase ofthe beams of light.
 3. An optical information recording and reproducingapparatus for recording information in and reproducing information froman optical information recording medium having reflecting layer andinformation recording layer in which information is recorded utilizingholography, the apparatus comprising: a pick-up device provided in aface-to-face relationship with the optical information recording medium,the pick-up device comprising: a light source; an information lightgeneration means for generating information light carrying twodimensional digital pattern information using the beams of light emittedby the light source; a recording reference light generation meansincluding modulation means for spatially modulating the beams of lightemitted by the light source, for generating reference light forrecording being spatially modulated by the modulation means; a recordingoptical system including only one objective lens for projecting theinformation light generated by the information light generation meansand the reference light for recording generated by the recordingreference light generation means upon the optical information recordingmedium, for illuminating the information recording layer on the sameside thereof with the information light and the reference light forrecording such that the information is recorded in the informationrecording layer in the form of an interference pattern as a result ofusing the reflecting layer as a reference plane to generate interferencebetween the information light and the reference light for recording, therecording optical system projects the information light and thereference light for recording such that a first optical axis of theinformation light and a second optical axis of the reference light forrecording are located on a first same line, a reproduction referencelight generation means including modulation means for spatiallymodulating the beams of light in a same manner in which the referencelight for recording was modulated when the information was recorded, forgenerating reference light for reproduction being spatially modulated bythe modulation means of the reproduction reference light generationmeans; a reproducing optical system including the objective lens forprojecting the reference light for reproduction generated by thereproduction reference light generation means upon the opticalinformation recording medium and for collecting reproduction lightgenerated at the information recording layer when illuminated with thereference light for reproduction, for illuminating the informationrecording layer with the reference light for reproduction and forcollecting the reproduction light on a same side of the informationrecording layer that is illuminated with the reference light forreproduction, wherein the reproducing optical system projects thereference light for reproduction and collects the reproduction lightsuch that a third optical axis of the reference light for reproductionand a fourth optical axis of the reproduction light are located on asecond same line; and a detection means for detecting the reproductionlight collected by the reproducing optical system.
 4. An opticalinformation recording and reproducing apparatus according to claim 3,wherein the information light generation means spatially modulates thebeams of light emitted by the light source to generate the informationlight carrying two dimensional digital pattern information.
 5. Anoptical information recording and reproducing apparatus according toclaim 3, wherein the modulation means of the recording reference lightgeneration means modulates the phase of the beams of light and themodulation means of the reproducing reference light generation meansmodulates the phase of the beams of light.
 6. An optical informationrecording and reproducing apparatus according to claim 3, wherein therecording optical system and the reproducing optical system arecomprised in a same device.
 7. An optical informationrecording/reproducing apparatus for recording information in an opticalinformation recording medium having reflecting layer and informationrecording layer in which information is recorded utilizing holographyand for reproducing the information from the optical informationrecording medium, the apparatus comprising a pick-up device provided ina face-to-face relationship with the optical information recordingmedium, the pick-up device having: a light source, an information lightgeneration means for generating information light carrying twodimensional digital pattern information by spatially modulating thebeams of light emitted by the light source; a recording reference lightgeneration means for generating reference light for recording using thebeams of light emitted by the light source; a reproduction referencelight generation means for generating reference light for reproductionusing the beams of light emitted by the light source; arecording/reproducing optical system including only one objective lens,for: (a) illuminating through the objective lens to the informationrecording layer with the information light generated by the informationlight generation means and the reference light for recording generatedby the recording reference light generation means such that theinformation is recorded in the information recording layer in the formof an interference pattern as a result of using the reflecting layer asa reference plane to generate interference between the information lightand the reference light for recording; (b) illuminating through theobjective lens to the information recording layer with the referencelight for reproduction generated by the reproduction reference lightgeneration means; and (c) collecting through the objective lensreproduction light generated at the information recording layer whenilluminated with the reference light for reproduction on a same side ofthe information recording layer that is illuminated with the referencelight for reproduction; and a detection means for detecting thereproduction light collected by the recording/reproducing opticalsystem, wherein the recording/reproducing optical system projects theinformation light and the reference light for recording such that afirst optical axis of the information light and a second optical axis ofthe reference light for recording are located on a first same line, andthe recording/reproducing optical system projects the reference lightfor reproduction and collects the reproduction light such that a thirdoptical axis of the reference light for reproduction and a fourthoptical axis of the reproduction light are located on a second sameline.
 8. An optical information reproducing apparatus for reproducinginformation from an optical information recording medium havingreflecting layer and information recording layer in which information isrecorded utilizing holography, the apparatus comprising: a pick-updevice provided in a face-to-face relationship with the opticalinformation recording medium, the pick-up device comprising: a lightsource; a reproduction reference light generation means includingmodulation means for spatially modulating the beams of light emitted bythe light source in the same manner in which the reference light wasmodulated when the information was recorded, for generating referencelight for reproduction being spatially modulated by the modulationmeans; a reproducing optical system including only one objective lensprojecting the reference light for reproduction generated by thereproduction reference light generation means upon the opticalinformation recording medium using the reflecting layer as a referenceplane to generate reproduction light and for collecting reproductionlight generated at the information recording layer when illuminated withthe reference light for reproduction, for illuminating the informationrecording layer with the reference light for reproduction and forcollecting the reproduction light on a same side of the informationrecording layer that is illuminated with the reference light forreproduction; a detection means for detecting the reproduction lightcollected by the reproducing optical system, wherein the reproducingoptical system projects the reference light for reproduction andcollects the reproduction light such that an optical axis of thereference light for reproduction and an optical axis of the reproductionlight are located on a same line.
 9. An optical information reproducingapparatus according to claim 8, wherein the modulation means of thereproducing reference light generation means modulates the phase of thebeams of light.
 10. An optical information recording apparatus forrecording information in a recording medium having reflecting layer andinformation recording layer in which information is recorded utilizingholography, the apparatus comprising: a pick-up device provided in aface-to-face relationship with the recording medium, the pick-up devicecomprising: a light source; a servo light source that emits servo lightonto the reflecting layer; a detection means for detecting reflectedservo light that is carrying information of the recording medium,reflected by the reflecting layer such that an optical axis of the servolight and an optical axis of the reflected servo light are located on asame line; an information light generation means for generatinginformation light carrying two dimensional digital pattern informationusing the beams of light emitted by the light source; a recordingreference light generation means including modulation means forspatially modulating the beams of light emitted by the light source, forgenerating reference light for recording being spatially modulated bythe modulation means; and a recording optical system including only oneobjective lens for projecting the information light generated by theinformation light generation means and the reference light for recordinggenerated by the recording reference light generation means onto therecording medium, for illuminating the information recording layer onthe same side thereof with the information light and the reference lightfor recording such that the information is recorded in the informationrecording layer in the form of a three dimensional interference patternas a result of using the reflecting layer as a reference plane togenerates interference between the information light and the referencelight for recording, wherein the recording optical system projects theinformation light and the reference light for recording such that anoptical axis of the information light and an optical axis of thereference light for recording are located on a same line.
 11. An opticalinformation recording and reproducing apparatus for recordinginformation in and reproducing information from an optical informationrecording medium having reflecting layer and information recording layerin which information is recorded utilizing holography, the apparatuscomprising: a pick-up device provided in a face-to-face relationshipwith the optical information recording medium, the pick-up devicecomprising: a light source; a servo light source that emits first servolight and second servo light onto the reflecting layer; a detectionmeans for detecting first reflected servo light which is carryinginformation of the medium, reflected by the reflecting layer such thatan optical axis of the first servo light and an optical axis of thefirst reflected servo light are located on a same line; an informationlight generation means for generating information light carrying twodimensional digital pattern information using the beams of light emittedby the light source; a recording reference light generation meansincluding modulation means for spatially, modulating the beams of lightemitted by the light source, for generating reference light forrecording being spatially modulated by the modulation means; a recordingoptical system including only one objective lens for projecting theinformation light generated by the information light generation meansand the reference light for recording generated by the recordingreference light generation means onto the optical information recordingmedium, for illuminating the information recording layer on the sameside thereof with the information light and the reference light forrecording such that the information is recorded in the informationrecording layer in the form of a three dimensional interference patternas a result of using the reflecting layer as a reference plane togenerate interference between the information light and the referencelight for recording, wherein the recording optical system projects theinformation light and the reference light for recording such that afirst optical axis of the information light and a second optical axis ofthe reference light for recording are located on a first same line; adetection means for detecting second reflected servo light that iscarrying information of the medium, reflected by the reflecting layersuch that an optical axis of the second servo light and an optical axisof the second reflected servo light are located on a same line; areproduction reference light generation means including modulation meansfor spatially modulating the beams of light in a same manner in whichthe reference light was modulated when the information was recorded, forgenerating reference light for reproduction being spatially modulated bythe modulation means of the reproduction reference light generationmeans; a reproducing optical system including the objective lens forprojecting the reference light for reproduction generated by thereproduction reference light generation means onto the opticalinformation recording medium and for collecting reproduction lightgenerated at the information recording layer when illuminated with thereference light for reproduction, for illuminating the informationrecording layer with the reference light for reproduction and forcollecting the reproduction light on a same side of the informationrecording layer that is illuminated with the reference light forreproduction, wherein the reproducing optical system projects thereference light for reproduction and collects the reproduction lightsuch that a third optical axis of the reference light for reproductionand a fourth optical axis of the reproduction light are located on asecond same line; and a detection means for detecting the reproductionlight collected by the reproducing optical system.
 12. An opticalinformation recording/reproducing apparatus for recording information inan optical information recording medium having reflecting layer andinformation recording layer in which information is recorded utilizingholography and for reproducing the information from the opticalinformation recording medium, the apparatus comprising: a pick-up deviceprovided in a face-to-face relationship with the optical informationrecording medium, the pick-up device having; a light source; a servolight generation means for generating servo light; a detection means fordetecting reflected servo light that is carrying information of themedium, reflected by the reflecting layer such that an optical axis ofthe servo light and an optical axis of the reflected servo light arelocated on a same line; an information light generation means forgenerating information light carrying two dimensional digital patterninformation by spatially modulating the beams of light emitted by thelight source, based on the information of the medium; a recordingreference light generation means for generating reference light forrecording using the beams of light emitted by the light source, based onthe information of the medium; a reproduction reference light generationmeans for generating reference light for reproduction using the beams oflight emitted by the light source, based on the information of themedium; a recording/reproducing optical system including only oneobjective lens, for: (a) illuminating through the objective lens to theinformation recording layer with the information light generated by theinformation light generation means and the reference light for recordinggenerated by the recording reference light generation means such thatthe information is recorded in the information recording layer in theform of a three dimensional interference pattern as a result of usingthe reflecting layer as a reference plane to generate interferencebetween the information light and the reference light for recording; (b)illuminating through the objective lens to the information recordinglayer with the reference light for reproduction generated by thereproduction reference light generation means; and (c) collectingthrough the objective lens reproduction light generated from theinformation recording layer when illuminated with the reference lightfor reproduction on a same side of the information recording layer thatis illuminated with the reference light for reproduction; and adetection means for detecting the reproduction light collected by therecording/reproducing optical system; wherein the recording/reproducingoptical system projects the information light and the reference lightfor recording such that a first optical axis of the information lightand a second optical axis of the reference light for recording arelocated on a first same line, and the recording/reproducing opticalsystem projects the reference light for reproduction and collects thereproduction light such that a third optical axis of the reference lightfor reproduction and a fourth optical axis of the reproduction light arelocated on a second same line.
 13. An optical information reproducingapparatus according to claim 12, wherein the modulation means of thereproducing reference light generation means modulates the phase of thebeams of light.
 14. An optical information reproducing apparatus forreproducing information from an optical information recording mediumhaving reflecting layer and information recording layer in whichinformation is recorded utilizing holography, the apparatus comprising:a pick-up device provided in a face-to-face relationship with theoptical information recording medium, the pick-up device comprising: alight source; a servo light source that emits servo light onto thereflecting layer; a detection means for detecting reflected servo lightthat is carrying information of the medium, reflected by the reflectinglayer such that an optical axis of the servo light and an optical axisof the reflected servo light are located on a same line; a reproductionreference light generation means including modulation means forspatially modulating the beams of light emitted by the light source inthe same manner in which the reference light was modulated when theinformation was recorded, for generating reference light forreproduction being spatially modulated by the modulation means; areproducing optical system including only one objective lens forprojecting the reference light for reproduction generated by thereproduction reference light generation means onto the opticalinformation recording medium and collecting reproduction light generatedfrom the information recording layer when illuminated with the referencelight for reproduction, for illuminating the information recording layerwith the reference light for reproduction and for collecting thereproduction light on a same side of the information recording layerthat is illuminated with the reference light for reproduction; adetection means for detecting the reproduction light collected by thereproducing optical system, wherein the reproducing optical systemprojects the reference light for reproduction and collects thereproduction light such that an optical axis of the reference light forreproduction and an optical axis of the reproduction light are locatedon a same line.